Reflective mask blank for euv lithography and process for its production, as well as substrate with reflective layer for such mask blank and process for its production

ABSTRACT

Process for producing a substrate with reflective layer for EUVL, which comprises forming a reflective layer for reflecting EUV light on a substrate, wherein the reflective layer is a multilayer reflective film having a low refractive index layer and a high refractive index layer alternately stacked plural times by a sputtering method, and depending upon the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate at the surface of the multilayer reflective film, at least one layer among the respective layers constituting the multilayer reflective film is made to be a reflectivity distribution correction layer having a thickness distribution provided in a radial direction from the center of the substrate, to suppress the in-plane distribution of the peak reflectivity of light in the EUV wavelength region in a radial direction from the center of the substrate.

TECHNICAL FIELD

The present invention relates to a reflective mask blank for EUV(Extreme Ultraviolet) lithography (hereinafter referred to as “maskblank for EUVL” in this specification) to be used for the production ofsemiconductors, etc., and a process for its production.

Further, the present invention relates to a substrate with reflectivelayer for EUV lithography (EUVL), and a process for its production. Thesubstrate with reflective layer for EUVL is used as a precursor for themask blank for EUVL.

BACKGROUND ART

Heretofore, in the semiconductor industry, a photolithography methodemploying visible light or ultraviolet light has been used as atechnique to transfer a fine pattern required to form an integratedcircuit with a fine pattern on e.g. a silicon substrate. However, theconventional photolithography method has come close to its limit, whileminiaturization of semiconductor devices is being accelerated. In thecase of the photolithography method, the resolution limit of a patternis about ½ of the exposure wavelength. Even if an immersion method isemployed, the resolution limit is said to be about ¼ of the exposurewavelength, and even if an immersion method of ArF laser (wavelength:193 nm) is employed, about 45 nm is presumed to be the limit. Under thecircumstances, as an exposure technique for the next generationemploying an exposure wavelength shorter than 45 nm, EUV lithography isexpected to be prospective, which is an exposure technique employing EUVlight having a wavelength further shorter than ArF laser. In thisspecification, EUV light is meant for a light ray having a wavelengthwithin a soft X-ray region or within a vacuum ultraviolet region,specifically for a light ray having a wavelength of from about 10 to 20nm, particularly about 13.5 nm±0.3 nm (from about 13.2 to 13.8 nm).

EUV light is likely to be absorbed by all kinds of substances, and therefractive index of substances at such a wavelength is close to 1,whereby it is not possible to use a conventional dioptric system likephotolithography employing visible light or ultraviolet light.Therefore, in EUV lithography, a catoptric system, i.e. a combination ofa reflective photomask and a mirror, is employed.

A mask blank is a stacked member before pattering, to be employed forthe production of a photomask. In the case of an EUV mask blank, it hasa structure wherein a reflective layer to reflect EUV light and anabsorber layer to absorb EUV light, are formed in this order on asubstrate made of e.g. glass.

Usually, a protective layer is formed between the above-describedreflective layer and the absorber layer. Such a protective layer is oneto be provided for the purpose of protecting the reflective layer, sothat the reflective layer will not be damaged by an etching process tobe carried out for the purpose of forming a pattern on the absorberlayer.

As the reflective layer, it is common to use a multilayer reflectivefilm having a low refractive index layer with a low refractive index toEUV light and a high refractive index layer with a high refractive indexto EUV light, alternately stacked to have the light reflectivityimproved when its surface is irradiated with EUV light. Specifically assuch a multilayer reflective film, there is, for example, a Mo/Simultilayer reflective film having a molybdenum (Mo) layer as a lowrefractive index layer and a silicon (Si) layer as a high refractiveindex layer alternately stacked.

For the absorber layer, a material having a high absorption coefficientto EUV light, specifically e.g. a material containing chromium (Cr) ortantalum (Ta) as the main component, is used.

Usually, a protective layer is formed between the above-describedreflective layer and the absorber layer. Such a protective layer is oneto be provided for the purpose of protecting the reflective layer, sothat the reflective layer will not be damaged by an etching process tobe carried out for the purpose of forming a pattern on the absorberlayer. In Patent Document 1, it is proposed to use ruthenium (Ru) as thematerial for the protective layer. In Patent Document 2, a protectivelayer is proposed which is made of a ruthenium compound (Ru content: 10to 95 at %) containing Ru and at least one member selected from Mo, Nb,Zr, Y, B, Ti and La.

Further, as disclosed in Patent Document 3, in a mask blank for EUVL, ithas been problematic that in-plane distribution of the peak reflectivityin the EUV wavelength region results at the surface of a multilayerreflective film. When a reflectivity spectrum of light in the EUVwavelength region at the surface of the multilayer reflective film ismeasured, the value of reflectivity varies depending upon the wavelengthfor measurement, and has a local maximum value i.e. the peakreflectivity. If in-plane distribution of the peak reflectivity of lightin the EUV wavelength region at the surface of the multilayer reflectivefilm (i.e. such a state that the peak reflectivity varies depending uponthe locations on the multilayer reflective film) results, at the timewhen EUVL is carried out by using a mask for EUVL prepared from such amask blank for EUVL, in-plane distribution of the EUV exposure amountapplied to the resist on a wafer will result. This causes fluctuationsin the dimension of a pattern in the exposure field and thus becomes afactor to impair high precision patterning.

In Patent Document 3, the required value relating to the in-planeuniformity of the peak reflectivity of light in the EUV wavelengthregion at the surface of the multilayer reflective film is set to bewithin ±0.25%. Further, in a case where a protective layer is formed onthe multilayer reflective film, the required value relating to thein-plane uniformity of the peak reflectivity of light in the EUVwavelength region at the surface of the protective layer is set to bewithin ±0.25%.

Therefore, with respect to the in-plane uniformity of the peakreflectivity of light in the EUV wavelength region at the multilayerreflective film surface or at the protective layer surface, its range(the difference between the maximum value and the minimum value of thepeak reflectivity) is required to be within 0.5%.

Further, as disclosed in Patent Document 3, in a mask blank for EUVL, itis also problematic that in-plane distribution of the center wavelengthof reflected light, specifically, in-plane distribution of the centerwavelength of reflected light in the EUV wavelength region at themultilayer reflective film surface, results. Here, the center wavelengthof reflected light in the EUV wavelength region is, when the wavelengthscorresponding to FWHM (full width of half maximum) of the peakreflectivity in the reflectivity spectrum in the EUV wavelength regionare represented by λ1 and λ2, a wavelength that becomes the center valueof these wavelengths ((λ1+λ2)/2).

In Patent Document 3, the required value relating to the in-planeuniformity of the center wavelength of reflected light in the EUVwavelength region at the surface of the multilayer reflective film isset to be within ±0.03 nm. Further, in a case where a protective layeris formed on the multilayer reflective film, the required value relatingto the in-plane uniformity of the center wavelength at the surface ofthe protective layer is set to be within ±0.03 nm.

Therefore, with respect to the in-plane uniformity of the centerwavelength of reflected light in the EUV wavelength region at themultilayer reflective film surface or at the protective layer surface,its range (the difference between the maximum value and the minimumvalue of the center wavelength) is required to be within 0.06 nm.

One of causes for the above in-plane distribution of reflected light atthe surface of the multilayer reflective film i.e. the in-planedistribution of the peak reflectivity of light in the EUV wavelengthregion at the surface, and the in-plane distribution of the centerwavelength of reflected light in the EUV wavelength region at thesurface, is in-plane distribution of the thicknesses of the respectivelayers constituting the multilayer reflective film i.e. the thicknessesof low refractive index layers and high refractive index layers (PatentDocument 3). Further, as disclosed in Patent Document 4, fluctuation inthickness (i.e. in-plane distribution of thickness) of a capping layer(i.e. a protective layer) to be formed on the multilayer reflective filmwill also be a cause for fluctuation of reflected light in the EUVwavelength region (i.e. in-plane distribution of the peak reflectivityof light in the EUV wavelength region, or in-plane distribution of thecenter wavelength of reflected light in the EUV wavelength region).

Therefore, at the time of film formation for the respective layersconstituting the multilayer reflective film, or at the time of filmformation for the protective layer, it is required to form a filmuniformly in order not to bring about in-plane distribution in the filmthickness.

Patent Document 5 discloses a method of forming a multilayer reflectivefilm on a substrate, and a method of forming a capping layer on themultilayer reflective film, by means of an ion beam sputtering method.In such methods, while rotating the substrate about its center axis atthe center, ion beam sputtering is carried out by maintaining the anglebetween the normal line to the substrate and the sputtered particlesincident on the substrate to be a certain specific angle. Therefore, inthe methods disclosed in Patent Document 5, as shown in FIG. 1 of thesame Document, the sputtered particles will enter from an obliquedirection to the normal line to the substrate. The methods are a methodof forming a multilayer reflective film on a substrate having concavedefects on its surface, and a method of forming a capping layer on themultilayer reflective film. However, also in a case where no concavedefects are present on the substrate surface, it is desired to carry outthe sputtering method under such a condition that while rotating thesubstrate about its center axis at the center, the sputtered particleswill enter from an oblique direction to the normal line to thesubstrate, in order to form a film uniformly so as not to bring aboutin-plane distribution in the thickness of the multilayer reflective filmor the capping layer to be formed on the multilayer reflective film.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: JP-A-2002-122981-   Patent Document 2: JP-A-2005-268750-   Patent Document 3: JP-A-2009-260183-   Patent Document 4: JP-A-2008-277398-   Patent Document 5: JP-A-2009-510711

DISCLOSURE OF INVENTION Technical Problem

As mentioned above, heretofore, it has been considered possible toresolve not only the in-plane distribution of the center wavelength ofreflected light in the EUV wavelength region but also the in-planedistribution of the peak reflectivity of light in the EUV wavelengthregion, at the surface of the multilayer reflective film (at the surfaceof the protective layer in a case where the protective layer is formedon the multilayer reflective film), by making uniform the thicknesses ofthe respective layers constituting the multilayer reflective film andthe thickness of the protective layer in a case where the protectivelayer is formed on the multilayer reflective film.

However, it has been found that even in a case where the thicknesses ofthe respective layers constituting the multilayer reflective film (andthe thickness of the protective layer in a case where the protectivelayer is to be formed on the multilayer reflective film) are madeuniform to such a level that the range of the in-plane uniformity (thedifference between the maximum value and the minimum value of the centerwavelength) being within 0.06 nm is satisfied as the required valuerelating to the in-plane uniformity of the center wavelength ofreflected light in the EUV wavelength region, there is a case wherein-plane distribution exceeding the required value results in the peakreflectivity of light in the EUV wavelength region. When viewed in aradial direction from the center of the substrate on which themultilayer reflective film or the protective layer is formed, thisin-plane distribution has a specific tendency, and it is an in-planedistribution such that in a radial direction of the substrate, the peakreflectivity of light in the EUV wavelength region lowers from thecenter of the substrate towards the peripheral portion of the substrate.Also in Examples in Patent Document 3, a reflective mirror substrate (amultilayer reflective film and substrate with protective film) obtainedby forming a Mo/Si multilayer reflective film on a synthetic quartzglass substrate by an ion beam sputtering method, followed by forming aRu film as a protective film, is confirmed to have an in-planedistribution such that the peak reflectivity at the center of thesubstrate is high and the peak reflectivity at the peripheral portion islow. The in-plane distribution of the peak reflectivity is 1.2%, whichdoes not satisfy the required value relating to the in-plane uniformityof the peak reflectivity i.e. its range (the difference between themaximum value and the minimum value of the peak reflectivity) beingwithin 0.5%.

The cause for formation of in-plane distribution with the above specifictendency is not clearly understood, but it is considered to be relatedwith a fact that at the time of formation the respective layersconstituting the multilayer reflective film or at the time of formationof the protective layer, the sputtering method is carried out under sucha condition that while rotating the substrate about its center axis atthe center, the sputtered particles will enter from an oblique directionto the normal line to the substrate, so that the periodical fluctuationrange of the film formation rate along with the substrate rotation tendsto be large from the center of the substrate towards the peripheralportion.

In order to solve such a problem of the prior art, it is an object ofthe present invention to provide a mask blank for EUVL excellent in thein-plane uniformity of the peak reflectivity of light in the EUVwavelength region and excellent in the in-plane uniformity of the centerwavelength of reflected light in the EUV wavelength region, and aprocess for its production, as well as a substrate with reflective layerfor EUVL to be used for the production of the mask blank for EUVL, and aprocess for its production.

Solution to Problem

In order to accomplish the above object, the present invention providesa process (1) for producing a substrate with reflective layer for EUVlithography (EUVL), which comprises forming a reflective layer forreflecting EUV light on a substrate, wherein the reflective layer is amultilayer reflective film having a low refractive index layer and ahigh refractive index layer alternately stacked plural times by asputtering method, and depending upon the in-plane distribution of thepeak reflectivity of light in the EUV wavelength region in a radialdirection from the center of the substrate at the surface of themultilayer reflective film, at least one layer among the respectivelayers constituting the multilayer reflective film is made to be areflectivity distribution correction layer having a thicknessdistribution provided in a radial direction from the center of thesubstrate, to suppress and reduce the in-plane distribution of the peakreflectivity of light in the EUV wavelength region in a radial directionfrom the center of the substrate.

Further, the present invention provides a process (2) for producing asubstrate with reflective layer for EUV lithography (EUVL), whichcomprises forming a reflective layer for reflecting EUV light on asubstrate, and forming a protective layer for the reflective layer onthe reflective layer, wherein the reflective layer is a multilayerreflective film having a low refractive index layer and a highrefractive index layer alternately stacked plural times by a sputteringmethod, the protective layer is a Ru layer or a Ru compound layer formedby a sputtering method, and depending upon the in-plane distribution ofthe peak reflectivity of light in the EUV wavelength region in a radialdirection from the center of the substrate at the surface of theprotective layer, at least one layer among the respective layersconstituting the multilayer reflective film and the protective layer, ismade to be a reflectivity distribution correction layer having athickness distribution provided in a radial direction from the center ofthe substrate, to suppress and reduce the in-plane distribution of thepeak reflectivity of light in the EUV wavelength region in a radialdirection from the center of the substrate.

In the process (1) or (2) for producing a substrate with reflectivelayer for EUVL according to the present invention, it is preferred thatthe in-plane distribution of the peak reflectivity of light in the EUVwavelength region in a radial direction from the center of the substratein a case where the thickness distribution corresponding to thereflectivity distribution correction layer is not provided, is anin-plane distribution such that the peak reflectivity becomes low in aradial direction from the center of the substrate, and as the thicknessdistribution in a radial direction from the center of the substrate inthe reflectivity distribution correction layer, a thickness distributionsuch that the peak reflectivity of light in the EUV wavelength regionbecomes high in a radial direction from the center of the substrate, isprovided, to suppress and reduce the in-plane distribution of the peakreflectivity of light in the EUV wavelength region in a radial directionfrom the center of the substrate.

In the process (1) or (2) for producing a substrate with reflectivelayer for EUVL according to the present invention, it is preferred thatthe thickness of the reflectivity distribution correction layer isadjusted to be such a thickness that at the peripheral portion of thesubstrate, the peak reflectivity of light in the EUV wavelength regionbecomes to have a local maximum value, and the difference between thethickness of the reflectivity distribution correction layer at theperipheral portion of the substrate and the thickness of thereflectivity distribution correction layer at the center of thesubstrate, is set so that the difference between the maximum value andthe minimum value of the peak reflectivity in the in-plane distributionof the peak reflectivity of light in the EUV wavelength region in aradial direction from the center of the substrate in a case where thereflectivity distribution correction layer is provided, becomes to be atmost 0.3%.

In the process (1) or (2) for producing a substrate with reflectivelayer for EUVL according to the present invention, it is preferred thatthe change in the peak reflectivity of light in the EUV wavelengthregion in a radial direction from the center of the substrate, formed bythe thickness distribution in a radial direction from the center of thesubstrate, in the reflectivity distribution correction layer, is within2%.

In the process (1) for producing a substrate with reflective layer forEUVL according to the present invention, it is preferred that in themultilayer reflective film, the stacked number of repeating units of thelow refractive index layer and the high refractive index layer is from30 to 60, and at least one layer among layers formed by the stackednumber of repeating units being at most 20 from the uppermost layer ofthe multilayer reflective film, is made to be the reflectivitydistribution correction layer.

In the process (2) for producing a substrate with reflective layer forEUVL according to the present invention, it is preferred that in themultilayer reflective film, the stacked number of repeating units of thelow refractive index layer and the high refractive index layer is from30 to 60, and at least one layer among the protective layer and layersformed by the stacked number of repeating units being at most 20 fromthe uppermost layer of the multilayer reflective film, is made to be thereflectivity distribution correction layer.

In the process (1) or (2) for producing a substrate with reflectivelayer for EUVL according to the present invention, it is preferred thatthe multilayer reflective film is a Mo/Si multilayer reflective filmhaving a molybdenum (Mo) layer and a silicon (Si) layer alternatelystacked plural times, and at least one layer among Si layers in theMo/Si multilayer reflective film is made to be the reflectivitydistribution correction layer.

In this case, it is more preferred that a Si layer as the uppermostlayer among Si layers in the Mo/Si multilayer reflective film is made tobe the reflectivity distribution correction layer.

Further, the present invention provides a process (1) for producing areflective mask blank for EUV lithography (EUVL), which comprisesforming a reflective layer for reflecting EUV light on a substrate, andforming an absorber layer for absorbing EUV light on the reflectivelayer, wherein the reflective layer is a multilayer reflective filmhaving a low refractive index layer and a high refractive index layeralternately stacked plural times by a sputtering method, and dependingupon the in-plane distribution of the peak reflectivity of light in theEUV wavelength region in a radial direction from the center of thesubstrate at the surface of the multilayer reflective film, at least onelayer among the respective layers constituting the multilayer reflectivefilm, is made to be a reflectivity distribution correction layer havinga thickness distribution provided in a radial direction from the centerof the substrate, to suppress and reduce the in-plane distribution ofthe peak reflectivity of light in the EUV wavelength region in a radialdirection from the center of the substrate.

Further, the present invention provides a process (2) for producing areflective mask blank for EUV lithography (EUVL), which comprisesforming a reflective layer for reflecting EUV light on a substrate,forming a protective layer for the reflective layer on the reflectivelayer, and forming an absorber layer for absorbing EUV light on theprotective layer, wherein the reflective layer is a multilayerreflective film having a low refractive index layer and a highrefractive index layer alternately stacked plural times by a sputteringmethod, the protective layer is a Ru layer or a Ru compound layer formedby a sputtering method, and depending upon the in-plane distribution ofthe peak reflectivity of light in the EUV wavelength region in a radialdirection from the center of the substrate at the surface of theprotective layer, at least one layer among the respective layersconstituting the multilayer reflective film and the protective layer, ismade to be a reflectivity distribution correction layer having athickness distribution provided in a radial direction from the center ofthe substrate, to suppress and reduce the in-plane distribution of thepeak reflectivity of light in the EUV wavelength region in a radialdirection from the center of the substrate.

In the process (1) or (2) for producing a reflective mask blank for EUVLaccording to the present invention, a low reflective layer forinspection light to be used for inspection of a mask pattern may befurther formed on the absorber layer.

In the process (1) or (2) for producing a reflective mask blank for EUVLaccording to the present invention, it is preferred that the in-planedistribution of the peak reflectivity of light in the EUV wavelengthregion in a radial direction from the center of the substrate in a casewhere the thickness distribution corresponding to the reflectivitydistribution correction layer is not provided, is an in-planedistribution such that the peak reflectivity becomes low in a radialdirection from the center of the substrate, and as the thicknessdistribution in a radial direction from the center of the substrate inthe reflectivity distribution correction layer, a thickness distributionsuch that the peak reflectivity of light in the EUV wavelength regionbecomes high in a radial direction from the center of the substrate, isprovided, to suppress and reduce the in-plane distribution of the peakreflectivity of light in the EUV wavelength region in a radial directionfrom the center of the substrate.

In the process (1) or (2) for producing a reflective mask blank for EUVLaccording to the present invention, it is preferred that the thicknessof the reflectivity distribution correction layer is adjusted to be sucha thickness that at the peripheral portion of the substrate, the peakreflectivity of light in the EUV wavelength region becomes to have alocal maximum value, and the difference between the thickness of thereflectivity distribution correction layer at the peripheral portion ofthe substrate and the thickness of the reflectivity distributioncorrection layer at the center of the substrate, is set so that thedifference between the maximum value and the minimum value of the peakreflectivity in the in-plane distribution of the peak reflectivity oflight in the EUV wavelength region in a radial direction from the centerof the substrate in a case where the reflectivity distributioncorrection layer is provided, becomes to be at most 0.3%.

In the process (1) or (2) for producing a reflective mask blank for EUVLaccording to the present invention, it is preferred that the change inthe peak reflectivity of light in the EUV wavelength region in a radialdirection from the center of the substrate, formed by the thicknessdistribution in a radial direction from the center of the substrate, inthe reflectivity distribution correction layer, is within 2%.

In the process (1) for producing a reflective mask blank for EUVLaccording to the present invention, it is preferred that in themultilayer reflective film, the stacked number of repeating units of thelow refractive index layer and the high refractive index layer is from30 to 60, and at least one layer among layers formed by the stackednumber of repeating units being at most 20 from the uppermost layer ofthe multilayer reflective film, is made to be the reflectivitydistribution correction layer.

In the process (2) for producing a reflective mask blank for EUVLaccording to the present invention, it is preferred that in themultilayer reflective film, the stacked number of repeating units of thelow refractive index layer and the high refractive index layer is from30 to 60, and at least one layer among the protective layer and layersformed by the stacked number of repeating units being at most 20 fromthe uppermost layer of the multilayer reflective film, is made to be thereflectivity distribution correction layer.

In the process (1) or (2) for producing a reflective mask blank for EUVLaccording to the present invention, it is preferred that the multilayerreflective film is a Mo/Si multilayer reflective film having amolybdenum (Mo) layer and a silicon (Si) layer alternately stackedplural times, and at least one layer among Si layers in the Mo/Simultilayer reflective film is made to be the reflectivity distributioncorrection layer.

In this case, it is more preferred that a Si layer as the uppermostlayer among Si layers in the Mo/Si multilayer reflective film is made tobe the reflectivity distribution correction layer.

Further, the present invention provides a substrate with reflectivelayer for EUVL, produced by the process (1) or (2) for producing asubstrate with reflective layer for EUVL according to the presentinvention.

Further, the present invention provides a reflective mask blank forEUVL, produced by the process (1) or (2) for producing a reflective maskblank for EUVL according to the present invention.

Further, the present invention provides a substrate with reflectivelayer (1) for EUV lithography (EUVL), which comprises a substrate and areflective layer for reflecting EUV light formed on the substrate,wherein the reflective layer is a multilayer reflective film having alow refractive index layer and a high refractive index layer alternatelystacked plural times, and at least one layer among the respective layersconstituting the multilayer reflective film is a reflectivitydistribution correction layer having a thickness distribution such thatthe thickness increases or decreases within a range of from 0.1 to 1 nmin a radial direction from the center of the substrate.

Further, the present invention provides a substrate with reflectivelayer (2) for EUV lithography (EUVL), which comprises a substrate, areflective layer for reflecting EUV light formed on the substrate, and aprotective layer for the reflective layer formed on the reflectivelayer, wherein the reflective layer is a multilayer reflective filmhaving a low refractive index layer and a high refractive index layeralternately stacked plural times, and at least one layer among therespective layers constituting the multilayer reflective film and theprotective layer is a reflectivity distribution correction layer havinga thickness distribution such that the thickness increases or decreaseswithin a range of from 0.1 to 1 nm in a radial direction from the centerof the substrate.

In the substrate with reflective layer (1) or (2) for EUVL according tothe present invention, it is preferred that the multilayer reflectivefilm is a Mo/Si multilayer reflective film having a molybdenum (Mo)layer and a silicon (Si) layer alternately stacked plural times, and atleast one layer among Si layers in the Mo/Si multilayer reflective filmis the reflectivity distribution correction layer.

In this case, it is more preferred that a Si layer as the uppermostlayer among Si layers in the Mo/Si multilayer reflective film is thereflectivity distribution correction layer.

Further, the present invention provides a reflective mask blank (1) forEUV lithography (EUVL), which comprises a substrate, a reflective layerfor reflecting EUV light formed on the substrate, and an absorber layerfor absorbing EUV light formed on the reflective layer, wherein thereflective layer is a multilayer reflective film having a low refractiveindex layer and a high refractive index layer alternately stacked pluraltimes, and at least one layer among the respective layers constitutingthe multilayer reflective film is a reflectivity distribution correctionlayer having a thickness distribution such that the thickness increasesor decreases within a range of from 0.1 to 1 nm in a radial directionfrom the center of the substrate.

Further, the present invention provides a reflective mask blank (2) forEUV lithography (EUVL), which comprises a substrate, a reflective layerfor reflecting EUV light formed on the substrate, a protective layer forthe reflective layer formed on the reflective layer, and an absorberlayer for absorbing EUV light formed on the protective layer, whereinthe reflective layer is a multilayer reflective film having a lowrefractive index layer and a high refractive index layer alternatelystacked plural times, the protective layer is a Ru layer or a Rucompound layer, and at least one layer among the respective layersconstituting the multilayer reflective film and the protective layer isa reflectivity distribution correction layer having a thicknessdistribution such that the thickness increases or decreases within arange of from 0.1 to 1 nm in a radial direction from the center of thesubstrate.

In the reflective mask blank (1) or (2) for EUVL according to thepresent invention, it is preferred that the multilayer reflective filmis a Mo/Si multilayer reflective film having a molybdenum (Mo) layer anda silicon (Si) layer alternately stacked plural times, and at least onelayer among Si layers in the Mo/Si multilayer reflective film is thereflectivity distribution correction layer.

In this case, it is more preferred that a Si layer as the uppermostlayer among Si layers in the Mo/Si multilayer reflective film is thereflectivity distribution correction layer.

In the reflective mask blank (1) or (2) for EUVL according to thepresent invention, a low reflective layer for inspection light to beused for inspection of a mask pattern may be formed on the absorberlayer.

Further, the present invention provides a reflective mask for EUVlithography obtained by patterning the reflective mask blank (1) or (2)for EUVL according to the present invention.

Advantageous Effects of Invention

According to the present invention, it is possible to produce areflective mask blank for EUVL and a substrate with reflective layer forEUVL, excellent in the in-plane uniformity of the peak reflectivity oflight in the EUV wavelength region and in the in-plane uniformity of thecenter wavelength of reflected light in the EUV wavelength region, atthe surface of the multilayer reflective film.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic cross-sectional view illustrating an embodiment ofthe reflective mask blank for EUVL to be produced by the process of thepresent invention.

FIG. 2 is an illustrative view showing the procedure for spin filmformation.

FIG. 3 is a graph showing the relation between the thickness of theuppermost Si layer in a Mo/Si multilayer reflective film and the peakreflectivity of light in the EUV wavelength region at the surface of theMo/Si multilayer reflective film.

FIG. 4 is a schematic cross-sectional view illustrating anotherembodiment of the reflective mask blank for EUVL to be produced by theprocess of the present invention.

FIG. 5 is a graph showing the relation between the location in a radialdirection from the center of the substrate and the in-plane distributionof the peak reflectivity of light in the EUV wavelength region at thesurface of a Mo/Si multilayer reflective film, in Comparative Example 1and Example 1. “Before correction” represents the results in ComparativeExample 1 and “After correction” represents the results in Example 1.

FIG. 6 is a graph showing the relation between the location in a radialdirection from the center of the substrate and the in-plane distributionof the peak reflectivity of light in the EUV wavelength region at thesurface of a Mo/Si multilayer reflective film, in Comparative Example 2and Example 2. “Before correction” represents the results in ComparativeExample 2 and “After correction” represents the results in Example 2.

FIG. 7 is a graph showing the relation between the location in a radialdirection from the center of the substrate and the in-plane distributionof the peak reflectivity of light in the EUV wavelength region at thesurface of a Mo/Si multilayer reflective film, in Comparative Example 3and Example 3. “Before correction” represents the results in ComparativeExample 3 and “After correction” represents the results in Example 3.

FIG. 8 is a graph showing the relation between the location in a radialdirection from the center of the substrate and the in-plane distributionof the peak reflectivity of light in the EUV wavelength region at thesurface of a Mo/Si multilayer reflective film, in Comparative Example 4and Example 4. “Before correction” represents the results in ComparativeExample 4 and “After correction” represents the results in Example 4.

DESCRIPTION OF EMBODIMENTS

Now, the present invention will be described with reference to thedrawings.

FIG. 1 is a schematic cross-sectional view illustrating an embodiment ofthe reflective mask blank for EUVL to be produced by the process of thepresent invention (hereinafter referred to as “the reflective mask blankfor EUVL of the present invention” in this specification). Thereflective mask blank 1 for EUVL shown in FIG. 1 has a reflective layer12 for reflecting EUV light and an absorber layer 14 for absorbing EUVlight formed in this order on a substrate 11. Between the reflectivelayer 12 and the absorber layer 14, a protective layer 13 is formed forprotecting the reflective layer 12 during formation of a pattern in theabsorber layer 14.

Here, in the reflective mask blank for EUVL of the present invention, inthe construction as shown in FIG. 1, only the substrate 11, thereflective layer 12 and the absorber layer 14 are essential, and theprotective layer 13 is an optional constituting element.

Now, the individual constituting elements of the reflective mask blank 1for EUVL will be described.

The substrate 11 is required to satisfy the properties as a substratefor a reflective mask blank for EUVL.

Therefore, the substrate 11 is preferably one having a low thermalexpansion coefficient (preferably 0±1.0×10⁻⁷/° C., more preferably0±0.3×10⁻⁷/° C., further preferably 0±0.2×10⁻⁷/° C., still furtherpreferably 0±0.1×10⁻⁷/° C., particularly preferably 0±0.05×10⁻⁷/° C.)and being excellent in smoothness, planarity and durability against acleaning liquid to be used for e.g. cleaning a mask blank or a photomaskafter patterning. As the substrate 11, specifically, a glass having alow thermal expansion coefficient, such as a SiO₂—TiO₂ type glass, maybe used. However, the substrate is not limited thereto, and it ispossible to employ a substrate of e.g. crystallized glass havingβ-quartz solid solution precipitated, quartz glass, silicon, or a metal.Further, a film such as a stress correcting film may be formed on thesubstrate 11.

The substrate 11 preferably has a smooth surface having a surfaceroughness of at most 0.15 nm rms and a flatness of at most 100 nm,whereby a high reflectivity and transfer precision can be attained by aphotomask after forming a pattern.

The size, thickness, etc. of the substrate 11 may suitably be determineddepending upon e.g. the designed values for the mask. In Examples givenhereinafter, a SiO₂—TiO₂ type glass having a size of 6 inches (152 mm)square and a thickness of 0.25 inch (6.35 mm) was used.

It is preferred that no defect is present on the film-forming surface ofthe substrate 11 i.e. the surface of the substrate 11 on the side wherea reflective layer 12 is to be formed. However, even in a case where adefect is present, in order not to cause a phase defect due to a concavedefect and/or a convex defect, it is preferred that the depth of aconcave defect or the height of a convex defect is not more than 2 nm,and the half value width of such a concave defect or convex defect isnot more than 60 nm.

The property particularly required for the reflective layer 12 of thereflective mask blank for EUVL is a high EUV light reflectivity.Specifically, when a light ray within the EUV wavelength region isapplied at an incident angle of 6° to the surface of the reflectivelayer 12, the peak reflectivity of light in the EUV wavelength region(i.e. the local maximum value of the reflectivity of the light ray inthe vicinity of a wavelength of 13.5 nm, which will be hereinafterreferred to as “the peak reflectivity of the EUV light” in thisspecification) is preferably at least 60%, more preferably at least 63%,further preferably at least 65%. Further, even in a case where aprotective layer 13 is formed on the reflective layer 12, the peakreflectivity of the EUV light is preferably at least 60%, morepreferably at least 63%, further preferably at least 65%.

Further, for the reflective layer 12 of the reflective mask blank forEUVL, the required value of the in-plane uniformity of the peakreflectivity of the EUV light is within 0.5% as its range (thedifference between the maximum value and the minimum value of the peakreflectivity). Further, in a case where a protective layer 13 is formedon the reflective layer 12, the required value of the in-planeuniformity of the peak reflectivity of the EUV light at the surface ofthe protective layer 13 is within 0.5% as its range (the differencebetween the maximum value and the minimum value of the peakreflectivity).

Further, for the reflective layer 12 of the reflective mask blank forEUVL, the required value of the in-plane uniformity of the centerwavelength of reflected light in the EUV wavelength region is within0.06 nm as its range (the difference between the maximum value and theminimum value of the center wavelength). Further, in a case where aprotective layer 13 is formed on the reflective layer 12, the requiredvalue of the in-plane uniformity of the center wavelength of reflectedlight in the EUV wavelength region at the surface of the protectivelayer 13 is within 0.06 nm as its range (the difference between themaximum value and the minimum value of the peak reflectivity).

As a reflective layer of a reflective mask blank for EUVL, a multilayerreflective film having a low refractive index layer as a layer to show alow refractive index to EUV light and a high refractive index layer as alayer to show a high refractive index to EUV light alternately stackedplural times is widely used, since a high reflectivity can thereby beaccomplished in the EUV wavelength region. As such a multilayerreflective film, a Mo/Si multilayer reflective film having a molybdenum(Mo) layer as a low refractive index layer and a silicon (Si) layer as ahigh refractive index layer alternately stacked plural times, is usuallyemployed. Other examples of the multilayer reflective film may, forexample, be a Ru/Si multilayer reflective film having a ruthenium (Ru)layer as a low refractive index layer and a silicon (Si) layer as a highrefractive index layer alternately stacked plural times, a Mo/Bemultilayer reflective film having a molybdenum (Mo) layer as a lowrefractive index layer and a berylium (Be) layer as a high refractiveindex layer alternately stacked plural times, and a Mo compound/Sicompound multilayer reflective film having a molybdenum (Mo) compoundlayer as a low refractive index layer and a silicon (Si) compound layeras a high refractive index layer alternately stacked plural times.

Further, like a multilayer reflective film disclosed inJP-A-2006-093454, the multilayer reflective film may be one having aninterlayer such as a diffusion preventive layer or a film stressrelaxation layer formed between the low refractive index layer (Molayer) and the high refractive index layer (Si layer).

The thickness of the respective layers (a low refractive index layer anda high refractive index layer) constituting the multilayer reflectivefilm, and the stacked number of repeating units of the low refractiveindex layer and the high refractive index layer, vary depending upon theconstituting materials for the respective layers or the EUV lightreflectivity to be accomplished. In the case of the Mo/Si multilayerreflective film, however, in order to obtain a reflective layer 12having an EUV light peak reflectivity of at least 60%, for example, a Molayer having a thickness of 2.5 nm and a Si layer having a thickness of4.5 nm are stacked so that the stacked number of repeating units wouldbe from 30 to 60.

Further, the respective layers (a Mo layer and a Si layer) constitutingthe Mo/Si multilayer reflective film are adjusted so that (1) thethickness distribution of the respective layers is a uniform thicknessdistribution within from 0.4 to 0.3% from the requirement for theafter-mentioned wavelength distribution, (2) the respective thicknessesof the Mo layer and the Si layer are adjusted to be thicknesses wherebythe maximum reflectivity is obtainable from the adjustment of theafter-mentioned γ ratio, and (3) the total thickness (bilayer) of the Molayer and the Si layer is adjusted to be about 7 nm so that the centerwavelength of reflected light in the EUV wavelength region will be about13.5 nm.

Here, the respective layers (a low refractive index layer and a highrefractive index layer) constituting the multilayer reflective film maybe formed to have desired thicknesses by means of a sputtering methodsuch as a magnetron sputtering method or an ion beam sputtering method.For example, in the case of forming a Mo/Si multilayer reflective filmby means of an ion beam sputtering method, it is preferred that a Molayer is formed to have a thickness of 2.5 nm at an ion acceleratingvoltage of from 300 to 1,500 V and a film-deposition rate of from 1.8 to18.0 nm/min by using a Mo target as the target and an Ar gas (gaspressure: 1.3×10⁻² Pa to 2.7×10⁻² Pa) as the sputtering gas, and then, aSi layer is formed to have a thickness of 4.5 nm at an ion acceleratingvoltage of from 300 to 1,500 V and a film-deposition rate of from 1.8 to18.0 nm/min by using a Si target as the target and an Ar gas (gaspressure: 1.3×10⁻² Pa to 2.7×10⁻² Pa) as the sputtering gas. When thisoperation is taken as one cycle, the Mo/Si multilayer reflective film isformed by stacking the Mo layer and the Si layer by from 30 to 60cycles.

However, in order to satisfy the above-mentioned required value of thein-plane uniformity of the peak reflectivity of EUV light and therequired value relating to the in-plane uniformity of the centerwavelength of reflected light in the EUV wavelength region, it isrequired to form a film uniformly so as not to cause in-planedistribution in the thicknesses of the respective layers (a lowrefractive index layer and a high refractive index layer) constitutingthe multilayer reflective film.

In order to form the respective layers (a low refractive index layer anda high refractive index layer) constituting the multilayer reflectivefilm to have uniform thicknesses by means of a sputtering method such asa magnetron sputtering method or an ion beam sputtering method, it ispreferred that as shown in FIG. 2, while a substrate 11 is rotated aboutan axis (center axis) 30 passing through its center O, sputteredparticles 20 are permitted to enter from an oblique direction to thenormal line H to the substrate 11. The reason is such that it ispossible to make the thickness of each layer formed by the sputteringmethod uniform by adjusting the incident angle α of the sputteredparticles 20 to the normal line H.

Hereinafter, in this specification, the film-forming procedure as shownin FIG. 2 will be referred to as “spinning film formation”. Here, thecenter axis is an axis passing through the center of the substrate, andin a case where the substrate shape is circular like the substrate 11shown in FIG. 2, the center axis is an axis passing through the center Oof the circle, and in a case where the substrate shape is a square orrectangle, the center axis is an axis passing through the intersectionof diagonal lines of the square or rectangle.

In the foregoing, a method for carrying out film formation on a singlesubstrate has been exemplified. However, the method is not limitedthereto and may be a so-called a plural substrate film-forming methodwherein film formation is carried out simultaneously on pluralsubstrates. In the case of the plural substrate film-forming method, itis preferred to set the film-forming conditions which include not onlyrotation of substrates about their central axes but also movement ofrevolution of the substrates.

At the time of forming the respective layers (a low refractive indexlayer and a high refractive index layer) constituting the multilayerreflective film, it is possible to uniformly control the thicknesses ofthe respective layers to be formed by the sputtering method, by carryingout a spinning film formation as shown in FIG. 2 and adjusting theincident angle α of sputtered particles 20 to the normal line H.

With respect to the required value relating to the in-plane uniformityof the center wavelength of reflected light in the EUV wavelengthregion, it is shown in Comparative Example 1 given hereinafter that therespective layers of the Mo/Si multilayer reflective film are uniformlyformed to such an extent that its range (the difference between themaximum value and the minimum value of the center wavelength) beingwithin 0.06 nm is satisfied. In Comparative Example 1, the in-planedistribution of the center wavelength of reflected light in the EUVwavelength region is within 0.04 nm, which satisfies its range beingwithin 0.06 nm as the required value relating to the in-plane uniformityof the center wavelength of reflected light in the EUV wavelengthregion. Here, the above in-plane distribution (within 0.04 nm) of thecenter wavelength of reflected light in the EUV wavelength regioncorresponds to 0.04/13.53≈0.3% as the thickness distribution of abilayer composed of two layers of the Mo layer and the Si layer as thebasic construction of the Mo/Si multilayer film.

However, even in a case where the thicknesses of the respective layersof the Mo/Si multilayer reflective film are uniformly formed to such alevel that with respect to the required value relating to the in-planeuniformity of the center wavelength of reflected light in the EUVwavelength region, its range being within 0.06 nm is satisfied, theremay be a case where in-plane distribution exceeding the require valueresults in the peak reflectivity of EUV light. This is shown inComparative Example 1 given hereinafter (by a dashed line correspondingto “Before correction” in FIG. 5).

In FIG. 5, in-plane distribution is shown such that the peakreflectivity of EUV light lowers from the center of the substratetowards the peripheral portion of the substrate. The in-planedistribution of the peak reflectivity of EUV light exceeds 0.6% and assuch does not satisfy the required value relating to in-plane uniformityof the peak reflectivity i.e. its range (the difference between themaximum value and the minimum value of the peak reflectivity) beingwithin 0.5%.

In the present invention, at least one layer among the respective layers(low refractive index layers and high refractive index layers)constituting the multilayer reflective film is made to be a reflectivitydistribution correction layer having a thickness distribution providedin a radial direction from the center of the substrate, to suppress thein-plane distribution of the peak reflectivity of EUV light i.e. thein-plane distribution such that the peak reflectivity of EUV lightlowers from the center of the substrate towards the peripheral portionof the substrate. Therefore, in the reflectivity distribution correctionlayer, thickness distribution is provided so that the peak reflectivityof EUV light increases from the center of the substrate towards theperipheral portion of the substrate.

In this specification, the peripheral portion of the substrate is meantfor a peripheral portion of a region (an optical property evaluationregion) for evaluation of an optical property of the multilayerreflective film, such as the peak reflectivity of EUV light or thecenter wavelength of reflected light in the EUV wavelength region. Forexample, in the case of a substrate of a 152 mm square, its opticalproperty evaluation region is a region of a 142 mm square. The cornerportions of this region of a 142 mm square are located in the vicinityof 100 mm in a radial direction from the center of the substrate, andtherefore, the peripheral portion of the substrate is located in thevicinity of 100 mm in a radial direction from the center of thesubstrate.

The reason as to why at least one layer among the respective layers (lowrefractive index layers and high refractive index layers) constitutingthe multilayer reflective film is made to be a reflectivity distributioncorrection layer having a thickness distribution provided in a radialdirection from the center of the substrate, for the above mentionedpurpose of suppressing the in-plane distribution of the peakreflectivity of EUV light, is that, as shown in FIG. 3, the peakreflectivity of EUV light at the surface of the multilayer reflectivefilm, has a dependency on the thickness of each layer (a low refractiveindex layer or a high refractive index layer) constituting themultilayer reflective film.

FIG. 3 is a graph showing the relation between the film thickness of aSi layer as the outermost layer among the respective layers constitutingthe Mo/Si multilayer reflective film formed by repeating stack of Mo andSi alternately for 40 cycles, and the peak reflectivity of EUV light atthe surface of the Mo/Si multilayer reflective film. Here, the thicknessof Mo is 2.5 nm, and the thickness of Si except for the uppermost layeris 4.5 nm.

As shown in FIG. 3, the peak reflectivity of EUV light at the surface ofthe Mo/Si multilayer reflective film, has a dependency on the thicknessof the Si layer, and repeats rise and fall periodically between thelocal maximum value and the local minimum value. In FIG. 3, the relationbetween the film thickness of a Si layer as the outermost layer amongthe respective layers constituting the Mo/Si multilayer reflective filmand the peak reflectivity of EUV light at the surface of the Mo/Simultilayer reflective film, is shown, but the peak reflectivity of EUVlight at the surface of the Mo/Si multilayer reflective film also has adependency on the thickness of a Si layer other than the outermost layerand repeats rise and fall periodically between the local maximum valueand the local minimum value. The peak reflectivity of EUV light at thesurface of the Mo/Si multilayer reflective film also has a dependency onthe thickness of a Mo layer and repeats rise and fall periodicallybetween the local maximum value and the local minimum value.

Further, in FIG. 3, with respect to a Mo/Si multilayer reflective film,the relation between the thickness of the Si layer as the uppermostlayer and the peak reflectivity of EUV light at the surface of the Mo/Simultilayer reflective film, is shown, but also in a multilayerreflective film wherein the above-mentioned low refractive index layerand high refractive index layer are different from the Mo/Si multilayerreflective film, or one wherein a diffusion preventive layer is formedbetween the low refractive index layer and the high refractive indexlayer of the multilayer reflective film, the peak reflectivity of EUVlight at the surface of the multilayer reflective film, has a dependencyon the thickness of each layer (a low refractive index layer or a highrefractive index layer) constituting the multilayer reflective film.

In the present invention, in order to suppress the above-mentionedin-plane distribution of the peak reflectivity of EUV light i.e. thein-plane distribution wherein the peak reflectivity of EUV light lowersfrom the center of the substrate towards the peripheral portion of thesubstrate, at least one layer among the respective layers (lowrefractive index layers and high refractive index layers) constitutingthe multilayer reflective film, is made to be a reflectivitydistribution correction layer having a thickness distribution providedto increase the peak reflectivity in a radial direction from the centerof the substrate (in other words, a thickness distribution so that thepeak reflectivity lowers from the peripheral portion towards the centerof the substrate).

The thickness distribution to increase the peak reflectivity in a radialdirection from the center of the substrate may be set based on theabove-mentioned in-plane distribution of the peak reflectivity at thesurface of the multilayer reflective film and the above-mentionedthickness dependency in the layer being the reflectivity distributioncorrection layer (the thickness dependency shown in FIG. 3 in a casewhere the Si layer as the uppermost layer of the Mo/Si multilayerreflective film is made to be the reflectivity distribution correctionlayer).

In the present invention, a thickness distribution is provided to lowerthe peak reflectivity of EUV light from the peripheral portion of asubstrate towards the center of the substrate, and therefore, thethickness of the reflectivity distribution correction layer at theperipheral portion of the substrate is made to be in the vicinity of thethickness at which the peak reflectivity of EUV light becomes to have alocal maximum value. In Examples given hereinafter, the thickness of thereflectivity distribution correction layer (the Si layer as theuppermost layer in the Mo/Si multilayer reflective film) was made to be4.5 nm based on FIG. 3.

And, a thickness distribution may be provided in a radial direction sothat the thickness of the reflectivity distribution correction layerincreases or decreases towards the center of the substrate. Here, with aview to suppressing the above-mentioned in-plane distribution of thepeak reflectivity of EUV light, in a case where a thickness distributionis provided in a radial direction from the center of the substrate, itis preferred to set the difference between the thickness at theperipheral portion of the substrate and the thickness at the center ofthe substrate, so that the difference between the maximum value and theminimum value of the peak reflectivity becomes to be at most 0.3% in thein-plane distribution of the peak reflectivity of EUV light in a radialdirection from the center of the substrate.

As mentioned above, in the case of Comparative Example 1 givenhereinafter, the amount of decrease in the peak reflectivity from thecenter towards the peripheral portion of the substrate (the amount ofdecrease in the peak reflectivity to the maximum value of the peakreflectivity) as derived from the in-plane distribution of the peakreflectivity shown in FIG. 5 becomes to be about 0.6%.

Therefore, the thickness at the center of the substrate may be set sothat in FIG. 3, the amount of decrease in the peak reflectivity to thelocal maximum value of the peak reflectivity will be about 0.6%.

Based on these premises, in Example 1, a thickness distribution in aradial direction was set so that the thickness of the Si layer as theuppermost layer in the Mo/Si multilayer reflective film became to be 4.5nm at the peripheral portion of the substrate, and the thickness of theSi layer as the uppermost layer in the Mo/Si multilayer reflective filmbecame to be 4.9 nm at the center of the substrate.

Here, in order to provide the above thickness distribution to the Silayer as the uppermost layer of the Mo/Si multilayer reflective film, atthe time of carrying out the spinning film formation as shown in FIG. 2,the incident angle α of sputtered particles 20 to the normal line H maysuitably be adjusted. For example, when the incident angle of sputteredparticles 20 at the time of a usual film formation is taken as thestandard, the incident angle of sputtered particles 20 at the time offorming the reflection distribution correction layer may be adjusted bygiving a difference of at least 10°, or in the case of imparting athickness distribution of at least 10%, the incident angle of sputteredparticles 20 at the time of forming the reflection distributioncorrection layer may be adjusted by giving a difference of at least 20°.Further, in Examples given hereinafter, the incident angle α wasadjusted within a range of from 0° to 60° to obtain a desired thicknessdistribution, and the in-plane distribution of the peak reflectivity ofEUV light was confirmed to be at most 0.3%.

However, if the change in the peak reflectivity of EUV light caused byproviding a thickness distribution in a radial direction from the centerof the substrate, is too large, an in-plane distribution is ratherlikely to be created in the peak reflectivity of EUV light. Therefore,the change in the peak reflectivity of EUV light caused by providing athickness distribution in a radial direction from the center of thesubstrate is preferably at most 2%, more preferably at most 1.5%,further preferably at most 1%.

As described above, in the present invention, at least one layer amongthe respective layers (low refractive index layers and high refractiveindex layers) constituting the multilayer reflective film, is made to bea reflectivity distribution correction layer having a thicknessdistribution provided to increase the peak reflectivity of EUV light ina radial direction from the center of the substrate (in other words, athickness distribution so that the peak reflectivity of EUV light lowersfrom the peripheral portion of the substrate towards the center of thesubstrate).

Therefore, any layer constituting the multilayer reflective film may bemade to be the above reflectivity distribution correction layer having athickness distribution provided. That is, a high refractive index layer(Si layer) may be made to be the above reflectivity distributioncorrection layer having a thickness distribution provided, or a lowrefractive index layer (Mo layer) may be made to be the abovereflectivity distribution correction layer having a thicknessdistribution provided.

Further, among the respective layers constituting the multilayerreflective film, only one layer may be made to be the above reflectivitydistribution correction layer having a thickness distribution provided,or two or more layers may be made to be such reflectivity distributioncorrection layers having a thickness distribution provided. Therefore,both of a high refractive index layer (Si layer) and a low refractiveindex layer (Mo layer) may be made to be such reflectivity distributioncorrection layers. Further, in a case where two or more layers are madeto be such reflectivity distribution correction layers having athickness distribution provided, mutually continuous two or more layersmay be made to be such reflectivity distribution correction layershaving a thickness distribution provided, or mutually separated two ormore layers may be made to be such reflectivity distribution correctionlayers having a thickness distribution provided.

Here, among the respective layers constituting the multilayer reflectivefilm, such a layer having a thickness distribution provided, is anexception to the above mentioned one construction example of a highrefractive index layer (Mo layer) and a low refractive index layer (Silayer) ((2.5 nm) and (4.5 nm)).

However, when a layer closer to the surface of the multilayer reflectivefilm is made to be such a layer having a thickness distributionprovided, the peak reflectivity of EUV light at the surface of themultilayer reflective film tends to change more in many cases.Therefore, it is preferred that at least one layer among layers formedby the stacked number of repeating units of a low refractive index layer(Mo layer) and a high refractive index layer (Si layer) being at most 20from the uppermost layer of the multilayer reflective film, is made tobe the above reflectivity distribution correction layer, it is morepreferred that at least one layer among layers formed by the stackednumber of repeating units being at most 10, is made to be the abovereflectivity distribution correction layer having a thicknessdistribution provided, and it is further preferred that at least onelayer among layers formed by the stacked number of repeating units beingat most 5, is made to be the above reflectivity distribution correctionlayer having a thickness distribution provided.

Here, the stacked number of repeating units of a Mo layer and a Si layerin the Mo/Si multilayer reflective film is from 30 to 60, as mentionedabove.

In the case of the Mo/Si multilayer reflective film, it is preferredthat among the layers constituting the Mo/Si multilayer reflective film,a Si layer is made to be the above reflectivity distribution correctionlayer having a thickness distribution provided. In thickness of therespective layers constituting the Mo/Si multilayer reflective film, theSi layer is thicker than the Mo layer, as shown in the above-mentionedone construction example (Mo layer (2.5 nm), Si layer (4.5 nm)). Thereason is that such a combination is preferred as the γ ratio (the ratioof the Si layer to the cycle length) to increase the peak reflectivityof EUV light. And, the Si layer having a larger thickness is capable ofchanging the peak reflectivity of EUV light at the surface of the Mo/Simultilayer reflective film by a smaller change in thicknessdistribution, whereby the thickness distribution can easily be adjustedwithin a control range of the film-forming apparatus, such beingpreferred. In a case where the reflection distribution correction layeris to be made of only one Si layer, when the uppermost Si layer iscounted as the first layer, the reflection distribution correction layermay be made of only one Si layer among the first to 30th layers (the30th to 60th layers depending upon the stacked number of repeating unitsof the Mo layer and the Si layer), preferably only one Si layer amongthe first to 20th layer, more preferably only one Si layer among thefirst to 10th layer, further preferably only one Si layer among thefirst to 5th layer, still further preferably only one Si layer among thefirst to third layers. Here, the above layer numbers of Si layers arelayer numbers when Mo layers are not counted. For example, in the caseof the Mo/Si multilayer reflective film wherein the uppermost layer is aSi layer, the second Si layer corresponds to the Si layer following theuppermost Si layer and Mo layer.

Further, in the Mo/Si multilayer reflective film, for example in a casewhere only the uppermost (first) Si layer is made to be the reflectivitydistribution correction layer, it is only required to change a conditionsuch as the incident angle of sputtered particles from the condition forfilm formation of other Si layers, only at the time of the final filmformation in the sputtering process, whereby there is a merit in thatthe film-forming process will not be cumbersome.

The protective layer 13 is provided for the purpose of protecting thereflective layer 12, so that at the time of forming a pattern in anabsorber layer 14 by an etching process, specifically a dry etchingprocess employing a chlorine-type gas as an etching gas, the reflectivelayer 12 will not be damaged by the etching process. Accordingly, as thematerial for the protective layer 13, a material hardly susceptible toan influence by the etching process of the absorber layer 14 i.e. havingan etching rate slower than the absorber layer 14 and hardly susceptibleto damage by such an etching process, is selected for use.

Further, the protective layer 13 is preferably configured such that theprotective layer 13 itself also has a high EUV light reflectivity inorder not to impair the EUV light reflectivity at the reflective layer12 even after forming the protective layer 13.

In the present invention, in order to satisfy the above conditions, asthe protective layer 13, a Ru layer or a Ru compound layer is formed.The Ru compound is preferably constituted by at least one memberselected from the group consisting of RuB, RuNb and RuZr. In a casewhere the protective layer 13 is a Ru compound layer, the content of Ruis preferably at least 50 at %, more preferably at least 80 at %,particularly preferably at least 90 at %. However, in a case where theprotective layer 13 is a RuNb layer, the content of Nb in the protectivelayer 13 is preferably from 5 to 40 at %, particularly preferably from 5to 30 at %.

In a case where a protective layer 13 is formed on the reflective layer12, the surface roughness of the surface of the protective layer 13 ispreferably at most 0.5 nm rms. If the surface roughness of the surfaceof the protective layer 13 is large, the surface roughness of theabsorber layer 14 to be formed on the protective layer 13 tends to belarge, whereby the edge roughness of a pattern to be formed on theabsorber layer 14 tends to be large, and the dimensional precision ofthe pattern tends to be poor. As the pattern becomes fine, the influenceof the edge roughness becomes distinct, and therefore, it is requiredthat the surface of the absorber layer 14 is smooth.

When the surface roughness of the surface of the protective layer 13 isat most 0.5 nm rms, the surface of the absorber layer 14 to be formed onthe protective layer 13 will be sufficiently smooth, thus being freefrom deterioration of the dimensional precision of a pattern due to aninfluence of the edge roughness. The surface roughness of the surface ofthe protective layer 13 is more preferably at most 0.4 nm rms, furtherpreferably at most 0.3 nm rms.

In a case where the protective layer 13 is formed on the reflectivelayer 12, the thickness of the protective layer 13 is preferably from 1to 10 nm in that it is thereby possible to increase the EUV lightreflectivity and to obtain an etching resistance property. The thicknessof the protective layer 13 is more preferably from 1 to 5 nm, furtherpreferably from 2 to 4 nm.

Further, in a case where the protective layer 13 is formed on thereflective layer (multilayer reflective film) 12, the above mentionedthickness distribution in a radial direction from the center of thesubstrate is provided to at least one layer among the protective layerand the respective layers (low refractive index layers and highrefractive index layers) constituting the multilayer reflective film.Therefore, the above thickness distribution may be provided to only theRu layer or the Ru compound layer formed as the protective layer 13.Otherwise, the above thickness distribution may be provided to both ofthe Ru layer or the Ru compound layer, and the respective layers (lowrefractive index layers and high refractive index layers) constitutingthe multilayer reflective film.

However, in a case where the reflective layer 12 is a Mo/Si multilayerreflective film, it is preferred to make the thickness of a Si layerlarger than the thickness of the Ru layer or the Ru compound layerformed as the protective layer 13, in order to increase the EUV lightreflectivity, and therefore, also in a case where the protective layer13 is formed on the reflective layer (Mo/Si multilayer reflective film)12, it is preferred to provide the thickness distribution to a Si layerconstituting the Mo/Si multilayer reflective film.

In the case of forming the protective layer 13 on the reflective layer12, the protective layer 13 is formed by means of a sputtering methodsuch as a magnetron sputtering method or an ion beam sputtering method.

In a case where a Ru layer is to be formed as the protective layer 13 bymeans of an ion beam sputtering method, discharge may be made in aninert gas atmosphere containing at least one of helium (He), argon (Ar),neon (Ne), krypton (Kr) and xenon (Xe) by using a Ru target as thetarget. Specifically, the ion beam sputtering may be carried out underthe following conditions.

Sputtering gas: Ar (gas pressure: from 1.3×10⁻² Pa to 2.7×10⁻² Pa)

Ion accelerating voltage: from 300 to 1,500 V

Film forming rate: from 1.8 to 18.0 nm/min

Here, also in a case where an inert gas other than Ar is used, the abovegas pressure applies.

Further, the state before forming the absorber layer of the reflectivemask blank for EUVL of the present invention, i.e. the structure havingthe absorber layer 14 excluded from the reflective mask blank 1 for EUVLshown in FIG. 1, is a substrate with reflective layer for EUVL of thepresent invention. The substrate with reflective layer for EUVL of thepresent invention is one constituting a precursor for a reflective maskblank for EUVL. However, the substrate with reflective layer for EUVL ofthe present invention is not limited to a precursor for a reflectivemask blank for EUVL and may generally be useful as an optical substratehaving a function to reflect EUV light.

In the substrate with reflective layer for EUVL of the presentinvention, at least one layer among the respective layers (lowrefractive index layers and high refractive index layers) constitutingthe multilayer reflective film is a reflectivity distribution correctionlayer having a thickness distribution such that the thickness increasesor decreases within a range of from 0.1 to 1 nm in a radial directionfrom the center of the substrate. Such a change in the thickness is morepreferably a thickness distribution such that the thickness continuouslyincreases or continuously decreases in a radial direction from thecenter of the substrate.

Further, in a case where a protective layer is formed on the reflectivelayer, at least one layer among the protective layer and the respectivelayers (low refractive index layers and high refractive index layers)constituting the multilayer reflective film is a reflectivitydistribution correction layer having a thickness distribution such thatthe thickness increases or decreases within a range of from 0.1 to 1 nmin a radial direction from the center of the substrate. Also in thiscase, the change in the thickness is more preferably a thicknessdistribution such that the thickness continuously increases orcontinuously decreases in a radial direction from the center of thesubstrate.

The property particularly required for the absorber layer 14 is that theEUV light reflectivity is very low. Specifically, the maximum lightreflectivity in the vicinity of a wavelength of 13.5 nm at the time ofirradiating the surface of the absorber layer 14 with a light ray in thewavelength region of EUV light, is preferably at most 0.5%, morepreferably at most 0.1%.

In order to attain the above property, the absorber layer 14 ispreferably made of a material having a high absorption coefficient ofEUV light and is preferably a layer containing at least Ta and N.

Further, the absorber layer 14 being a layer containing at least Ta andN is preferred also from such a viewpoint that it is thereby easy toform a film having a crystalline state being amorphous.

As the layer containing at least Ta and N, it is preferred to employ onemember selected from the group consisting of TaN, TaNH, TaBN, TaGaN,TaGeN, TaSiN, TaBSiN and PdTaN. Examples of such preferred compositionsfor the absorber layer are as follows.

TaN Layer

Content of Ta: preferably from 30 to 90 at %, more preferably from 40 to80 at %, further preferably from 40 to 70 at %, particularly preferablyfrom 50 to 70 at %

Content of N: preferably from 10 to 70 at %, more preferably from 20 to60 at %, further preferably from 30 to 60 at %, particularly preferablyfrom 30 to 50 at %

TaNH Layer

Total content of Ta and N: preferably from 50 to 99.9 at %, morepreferably from 90 to 98 at %, further preferably from 95 to 98 at %

Content of H: preferably from 0.1 to 50 at %, more preferably from 2 to10 at %, further preferably from 2 to 5 at %

Compositional ratio of Ta to N (Ta:N): preferably from 9:1 to 3:7, morepreferably from 7:3 to 4:6, further preferably from 7:3 to 5:5

TaBN Layer

Total content of Ta and N: preferably from 75 to 95 at %, morepreferably from 85 to 95 at %, further preferably from 90 to 95 at %

Content of B: preferably from 5 to 25 at %, more preferably from 5 to 15at %, further preferably from 5 to 10 at %

Compositional ratio of Ta to N (Ta:N): preferably from 9:1 to 3:7, morepreferably from 7:3 to 4:6, further preferably from 7:3 to 5:5

TaBSiN Layer

Content of B: at least 1 at % and less than 5 at %, preferably from 1 to4.5 at %, more preferably from 1.5 to 4 at %

Content of Si: from 1 to 25 at %, preferably from 1 to 20 at %, morepreferably from 2 to 12 at %

Compositional ratio of Ta to N (Ta:N): from 8:1 to 1:1

Content of Ta: preferably from 50 to 90 at %, more preferably from 60 to80 at %

Content of N: preferably from 5 to 30 at %, more preferably from 10 to25 at %

PdTaN Layer

Total content of Ta and N: preferably from 30 to 80 at %, morepreferably from 30 to 75 at %, further preferably from 30 to 70 at %

Content of Pd: preferably from 20 to 70 at %, more preferably from 25 to70 at %, further preferably from 30 to 70 at %

Compositional ratio of Ta to N (Ta:N): preferably from 1:7 to 3:1, morepreferably from 1:3 to 3:1, further preferably from 3:5 to 3:1

As mentioned above, if the surface roughness of the surface of theabsorber layer 14 is large, the edge roughness of a pattern to be formedon the absorber layer 14 tends to be large, and the dimensionalprecision of the pattern deteriorates. As the pattern becomes fine, theinfluence of the edge roughness becomes distinct, and therefore, thesurface of the absorber layer 14 is required to be smooth.

In a case where a layer containing at least Ta and N is formed as theabsorber layer 14, its crystal state is amorphous, and the surfacesmoothness is excellent. Specifically when a TaN layer is formed as theabsorber layer 14, the surface roughness of the surface of the absorberlayer 14 becomes to be at most 0.5 nm rms.

When the surface roughness of the surface of the absorber layer 14 is atmost 0.5 nm rms, the surface of the absorber layer 14 is sufficientlysmooth, whereby the dimensional precision is free from deterioration dueto an influence of an edge roughness. The surface roughness of theabsorber layer 14 is more preferably at most 0.4 nm rms, furtherpreferably at most 0.3 nm rms.

As a layer containing at least Ta and N, the absorber layer 14 has ahigh etching rate at the time when dry etching is carried out by using achlorine-type gas as the etching gas, and shows its etching selectivityto the protective layer 13 being at least 10. In this specification, theetching selectivity can be calculated by the following formula.

Etching selectivity=(etching rate of absorber layer 14)/(etching rate ofprotective layer 13)

The etching selectivity is preferably at least 10, more preferably atleast 11, particularly preferably at least 12.

The thickness of the absorber layer 14 is preferably at least 5 nm, morepreferably at least 20 nm, further preferably at least 30 nm,particularly preferably at least 50 nm.

On the other hand, if the thickness of the absorber layer 14 is toolarge, the precision of a pattern to be formed in the absorber layer 14tends to be low, and therefore, it is preferably at most 100 nm, morepreferably at most 90 nm, further preferably at most 80 nm.

For the absorber layer 14, it is possible to use a well-knownfilm-forming method, e.g. a sputtering method such as a magnetronsputtering method or an ion beam sputtering method.

In a case where a TaN layer is to be formed as the absorber layer 14, inthe case of using a magnetron sputtering method, the TaN layer may beformed by using a Ta target and letting the target discharge in anitrogen (N₂) atmosphere diluted by Ar.

In order to form a TaN layer as the absorber layer 14 by theabove-exemplified method, specifically the method may be carried outunder the following film-forming conditions.

Sputtering gas: mixed gas of Ar and N₂ (N₂ gas concentration: from 3 to80 vol %, preferably from 5 to 30 vol %, more preferably from 8 to 15vol %; gas pressure: from 0.5×10⁻¹ Pa to 10×10⁻¹ Pa, preferably from0.5×10⁻¹ Pa to 5×10⁻¹ Pa, more preferably from 0.5×10⁻¹ Pa to 3×10⁻¹ Pa)

Applied power (for each target): from 30 to 1,000 W, preferably from 50to 750 W, more preferably from 80 to 500 W

Film forming rate: from 2.0 to 60 nm/min, preferably from 3.5 to 45nm/min, more preferably from 5 to 30 nm/min.

Further, the reflective mask blank for EUVL of the present invention mayhave a constituting element other than the construction shown in FIG. 4(i.e. the substrate 11, the reflective layer 12, the protective layer 13and the absorber layer 14).

FIG. 4 is a schematic cross-sectional view illustrating anotherembodiment of the reflective mask blank for EUVL of the presentinvention.

In the reflective mask blank 1′ for EUVL as shown in FIG. 4, a lowreflective layer 15 for inspection light to be used for inspection of amask pattern is formed on the absorber layer 14.

In the preparation of a reflective mask for EUVL from the reflectivemask blank for EUVL of the present invention, after forming a pattern inthe absorber layer, inspection is carried out to see that this patternis formed as designed. In this inspection of the mask pattern, aninspection machine using light of usually 257 nm as inspection light, isemployed. That is, the inspection is made by the difference inreflectivity of such light of about 257 nm, specifically by thedifference in the reflectivity between a surface exposed by removal ofthe absorber layer 14 by patterning and the surface of the absorberlayer 14 remained without being removed by the patterning. Here, theformer is the surface of the protective layer 13, and in a case where noprotective layer 13 is formed on the reflective layer 12, it is thesurface of the reflective layer 12 (specifically the surface of a Silayer as the uppermost layer of the Mo/Si multilayer reflective film).

Therefore, if the difference in the reflectivity between the protectivelayer 13 surface (or the reflective layer 12 surface) and the absorberlayer 14 surface to the wavelength of inspection light of about 257 nm,is small, the contrast at the time of the inspection becomes poor, andan accurate inspection may not be possible.

The absorber layer 14 having the above-described construction has anextremely low EUV light reflectivity and has excellent properties as anabsorber layer for a reflective mask blank for EUVL, but from theviewpoint of the wavelength of inspection light, the light reflectivitymay not necessarily be sufficiently low. As a result, the differencebetween the reflectivity at the absorber layer 14 surface and thereflectivity at the reflective layer 12 surface (or the protective layer13 surface) at the wavelength of inspection light, tends to be small,and the contrast at the time of inspection may not sufficiently beobtainable. If the contrast at the time of inspection cannot besufficiently obtained, a defect in the pattern cannot be sufficientlydetected in the inspection of a mask, and an accurate inspection of adefect may not be carried out.

Like in the reflective mask blank 1′ for EUVL shown in FIG. 4, byforming a low reflective layer 15 on the absorber layer 14, the contrastat the time of inspection will be good. In other words, the lightreflectivity at the wavelength of inspection light becomes very low.With the low reflective layer 15 to be formed for such a purpose, themaximum light reflectivity at the wavelength of inspection light whenirradiated with light in the wavelength region (in the vicinity of 257nm) of inspection light, is preferably at most 15%, more preferably atmost 10%, further preferably at most 5%.

When the light reflectivity at the wavelength of inspection light at thelow reflective layer 15 is at most 15%, the contrast at the time of theinspection will be good. Specifically, the contrast between reflectedlight with a wavelength of the inspection light at the protective layer13 surface (or the reflective layer 12 surface) and reflected light withthe wavelength of the inspection light at the low reflective layer 15surface becomes at least 40%.

In this specification, the contrast is obtained by using the followingformula.

Contrast (%)=((R ₂ −R ₁)/(R ₂ +R ₁))×100

Here, R₂ at the wavelength of the inspection light is the reflectivityat the protective layer 13 surface (or the reflective layer 12 surface),and R₁ is the reflectivity at the surface of the low reflective layer15. Here, the above R₁ and R₂ are measured in such a state that apattern is formed in the absorber layer 14 and the low reflective layer15 of the reflective mask blank 1′ for EUVL shown in FIG. 4. The aboveR₂ is a value measured at the protective layer 13 surface (or thereflective layer 12 surface) exposed as the absorber layer 14 and thelow reflective layer 15 were removed by patterning, and R₁ is a valuemeasured at the surface of the low reflective layer 15 remained withoutbeing removed by patterning.

In the present invention, the contrast represented by the above formulais more preferably at least 45%, further preferably at least 60%,particularly preferably at least 70%.

To attain the above-described properties, the low reflective layer 15 ispreferably constituted by a material having a refractive index lowerthan the absorber layer 14 at the wavelength of inspection light, andits crystal state is preferably amorphous.

As a specific example of such a low reflective layer 15, one containingTa, oxygen (O) and nitrogen (N) in the following atomic ratio (lowreflective layer (TaON)) may be mentioned.

Content of Ta: from 20 to 80 at %, preferably from 20 to 70 at %, morepreferably from 20 to 60 at %

Total content of O and N: from 20 to 80 at %, preferably from 30 to 80at %, more preferably from 40 to 80 at %

Compositional ratio of O to N: from 20:1 to 1:20, preferably from 18:1to 1:18, more preferably from 15:1 to 1:15

With the above-described construction, the low reflective layer (TaON)is amorphous in its crystal state and is excellent in its surfacesmoothness. Specifically, the surface roughness of the low reflectivelayer (TaON) surface is at most 0.5 nm rms.

As mentioned above, in order to prevent deterioration in the dimensionalprecision of a pattern due to an influence of the edge roughness, it isrequired that the absorber layer 14 surface is smooth. The lowreflective layer 15 is formed on the absorber layer 15, and therefore,for the same reason, its surface is required to be smooth.

When the surface roughness of the low reflective layer 15 surface is atmost 0.5 nm rms, the low reflective layer 15 surface is sufficientlysmooth and free from deterioration in the dimensional precision of apattern due to an influence of the edge roughness. The surface roughnessof the low reflective layer 15 surface is more preferably at most 0.4 nmrms, further preferably at most 0.3 nm rms.

In a case where the low reflective layer 15 is formed on the absorberlayer 14, the total thickness of the absorber layer 14 and the lowreflective layer 15 is preferably from 20 to 130 nm. Further, if thethickness of the low reflective layer 15 is more than the thickness ofthe absorber layer 14, the EUV absorbing property at the absorber layer14 is likely to be low, and therefore, the thickness of the lowreflective layer 15 is preferably less than the thickness of theabsorber layer 14. For this reason, the thickness of the low reflectivelayer 15 is preferably from 5 to 30 nm, more preferably from 10 to 20nm.

The low reflective layer (TaON) having the above construction may beformed by a sputtering method such as a magnetron sputtering method oran ion beam sputtering method by using a Ta target in an atmosphere ofoxygen (O₂) and nitrogen (N₂) diluted with an inert gas containing atleast one of helium (He), argon (Ar), neon (Ne), krypton (Kr) and xenon(Xe). Otherwise, a Ta target may be discharged in a nitrogen (N₂)atmosphere diluted with an inert gas containing at least one of helium(He), argon (Ar), neon (Ne), krypton (Kr) and xenon (Xe) to form a filmcontaining Ta and N, and then the formed film is oxidized by e.g. beingexposed to oxygen plasma or being irradiated with an ion beam usingoxygen, to obtain the low reflective layer (TaON) having the aboveconstruction.

In order to form the low reflective layer (TaON) by the above method,specifically the following film-forming conditions may be employed.

Sputtering gas: mixed gas of Ar, O₂ and N₂ (O₂ gas concentration: from 5to 80 vol %, N₂ gas concentration: from 5 to 75 vol %, preferably O₂ gasconcentration: from 6 to 70 vol %, N₂ gas concentration: from 6 to 35vol %, more preferably O₂ gas concentration: from 10 to 30 vol %, N₂ gasconcentration: from 10 to 30 vol %, Ar gas concentration: from 5 to 90vol %, preferably from 10 to 88 vol %, more preferably from 20 to 80 vol%; gas pressure: from 1.0×10⁻¹ Pa to 50×10⁻¹ Pa, preferably from1.0×10⁻¹ Pa to 40×10⁻¹ Pa, more preferably from 1.0×10⁻¹ Pa to 30×10⁻¹Pa)

Applied power: from 30 to 1,000 W, preferably from 50 to 750 W, morepreferably from 80 to 500 W

Film forming rate: from 0.1 to 50 nm/min, preferably from 0.2 to 45nm/min, more preferably from 0.2 to 30 nm/min.

Here, in a case where an inert gas other than Ar is used, theconcentration of such an inert gas is adjusted to be within the sameconcentration range as the above Ar gas concentration. Further, in acase where plural types of inert gases are used, the total concentrationof such inert gases is adjusted to be within the same concentrationrange as the above Ar gas concentration.

Here, the reason as to why it is preferred to form a low reflectivelayer 15 on the absorber layer 14 as in the reflective mask blank 1′ forEUVL shown in FIG. 5, is that the wavelength of inspection light for apattern is different from the wavelength of EUV light. Therefore, in acase where EUV light (in the vicinity of 13.5 nm) is used as theinspection light for a pattern, it is considered unnecessary to form alow reflective layer 15 on the absorber layer 14. The wavelength ofinspection light tends to be shifted toward a low wavelength side as thesize of a pattern becomes small, and in future, it is considered to beshifted to 193 nm or further to 13.5 nm. Further, in the case where thewavelength of inspection light is 193 nm, it may not be required to forma low reflective layer 15 on the absorber layer 14. In the case wherethe wavelength of inspection light is 13.5 nm, it is consideredunnecessary to form a low reflective layer 15 on the absorber layer 14.

The reflective mask blank for EUVL of the present invention may have afunctional film commonly known in the field of reflective mask blanksfor EUVL, in addition to the reflective layer 12, the protective layer13, the absorber layer 14 and the low reflective layer 15. A specificexample of such a functional film may, for example, be an electricallyconductive coating formed on the rear side of a substrate to promote theelectrostatic chucking of the substrate, as disclosed in e.g.JP-A-2003-501823. Here, in the substrate 11 shown in FIG. 1, the rearside of the substrate means the surface on the opposite side to the sidewhere the reflective layer 12 is formed. For the electrically conductivecoating to be formed on the rear side of the substrate for such apurpose, the electrical conductivity and the thickness of theconstituting material are selected so that the sheet resistance will beat most 100Ω/□. The constituting material of the electrically conductivecoating may be selected widely from those disclosed in knownliteratures. For example, an electrically conductive (high dielectricconstant) coating disclosed in JP-A-2003-501823, specifically a coatingcomprising silicon, TiN, molybdenum, chromium and TaSi may be applied.The thickness of the electrically conductive coating may, for example,be from 10 to 1,000 nm.

The electrically conductive coating may be formed by means of a knownfilm-forming method e.g. a sputtering method, such as a magnetronsputtering method or an ion beam sputtering method, a CVD method, avacuum vapor deposition method or an electroplating method.

In the reflective mask blank for EUVL of the present invention, at leastone layer among the respective layers (low refractive index layers andhigh refractive index layers) constituting the multilayer reflectivefilm is a reflectivity distribution correction layer having a thicknessdistribution such that the thickness increases or decreases within arange of from 0.1 to 1 nm in a radial direction from the center of thesubstrate. Such a change in the thickness is more preferably a thicknessdistribution such that the thickness continuously increases orcontinuously decreases in a radial direction from the center of thesubstrate.

Further, in a case where a protective layer is formed on the reflectivelayer, at least one layer among the respective layers (low refractiveindex layers and high refractive index layers) constituting themultilayer reflective film and the protective layer is a reflectivitydistribution correction layer having a thickness distribution such thatthe thickness increases or decreases within a range of from 0.1 to 1 nmin a radial direction from the center of the substrate. Also in thiscase, the change in the thickness is more preferably a thicknessdistribution such that the thickness continuously increases orcontinuously decreases in a radial direction from the center of thesubstrate.

The reflective mask for EUVL may be produced by patterning at least theabsorber layer of the reflective mask blank for EUVL produced by theprocess of the present invention (in a case where a low reflective layeris formed on the absorber layer, the absorber layer and the lowreflective layer). The method for patterning the absorber layer (in acase where a low reflective layer is formed on the absorber layer, theabsorber layer and the low reflective layer), is not particularlylimited. For example, a method may be employed wherein a resist isapplied on the absorber layer (in a case where a low reflective layer isformed on the absorber layer, the absorber layer and the low reflectivelayer) to form a resist pattern, and by using it as a mask, the absorberlayer (in a case where a low reflective layer is formed on the absorberlayer, the absorber layer and the low reflective layer) is subjected toetching. The material for the resist, or the drawing method for theresist pattern may suitably be selected in consideration of e.g. thematerial of the absorber layer (in a case where a low reflective layeris formed on the absorber layer, the absorber layer and the lowreflective layer). As the method for etching the absorber layer (in acase where a low reflective layer is formed on the absorber layer, theabsorber layer and the low reflective layer), dry etching using achlorine-type gas as an etching gas may be employed. After patterningthe absorber layer (in a case where a low reflective layer is formed onthe absorber layer, the absorber layer and the low reflective layer),the resist is removed by a remover liquid to obtain the reflective maskfor EUVL.

EXAMPLES

Now, the present invention will be described in further detail withreference to Examples.

Comparative Example 1

In this Example, a substrate with reflective layer for EUVL wasprepared. This substrate with reflective layer for EUVL has a structurehaving the absorber layer 14 excluded from the mask blank 1 shown inFIG. 1.

As a substrate 11 for film formation, a SiO₂—TiO₂ type glass substrate(size: 6 inches (152 mm) square, thickness: 6.35 mm) is used. Thethermal expansion coefficient of this glass substrate is 0.05×10⁻⁷/° C.,the Young's modulus is 67 GPa, the Poisson ratio is 0.17, and thespecific rigidity is 3.07×10⁷ m²/s². This glass substrate was polishedto form a smooth surface having a surface roughness rms of at most 0.15nm and a planarity of at most 100 nm.

On the rear surface side of the substrate 11, a Cr film having athickness of 100 nm was formed by a magnetron sputtering method toprovide an electrically conductive coating (not shown in the drawings)having a sheet resistance of 100Ω/□.

By using the Cr film formed by the above procedure, the substrate 11(size: 6 inches (152 mm) square, thickness: 6.35 mm) was fixed to ausual electrostatic chuck of a flat plate shape, and on the surface ofthe substrate 11, by carrying out the spinning film formation as shownin FIG. 2, a Mo film and a Si film were alternately formed by means ofan ion beam sputtering method for 40 cycles to form a Mo/Si multilayerreflective film (reflective layer 12) having a total thickness of 280 nm((2.5 nm+4.5 nm)×40). Here, the uppermost layer of the Mo/Si multilayerreflective film is a Si film. The Mo/Si multilayer reflective layer wasformed in a 152 mm square region on the substrate 11 surface.

The film forming conditions for the Mo film and the Si film are asfollows.

Film Forming Conditions for Mo Film

-   -   Target: Mo target    -   Sputtering gas: mixed gas of Ar and H₂ (H₂ gas concentration: 3        vol %, Ar gas concentration: 97 vol %, gas pressure: 0.02 Pa)    -   Voltage: 700 V    -   Film forming rate: 3.84 nm/min.    -   Film thickness: 2.3 nm

Film Forming Conditions for Si Film

-   -   Target: Si target (boron-doped)    -   Sputtering gas: mixed gas of Ar and H₂ (H₂ gas concentration: 3        vol %, Ar gas concentration: 97 vol %, gas pressure: 0.02 Pa)    -   Voltage: 700 V    -   Film forming rate: 4.62 nm/min.    -   Film thickness: 4.5 nm

With respect to the Si layer as the uppermost layer in the Mo/Simultilayer reflective film formed by the above procedure, the thicknessdistribution in a radial direction from the center of the substrate wasevaluated by means of XRR (X-ray reflectivity method). The thicknessdistribution in a radial direction from the center of the substrate was0.0 nm.

To the surface of the Mo/Si multilayer reflective film formed by theabove procedure, EUV light was applied at an incident angle of 6°.Reflected light in the EUV wavelength region at that time was measuredby means of an EUV reflectivity meter (MBR, manufactured by AIXUV GmbH),whereupon the in-plane distribution of the peak reflectivity in the samewavelength region and the in-plane distribution of the center wavelengthof reflected light were evaluated.

The in-plane distribution of the center wavelength of reflected light inthe EUV wavelength region was within 0.04 nm, which satisfies therequired value relating to the in-plane uniformity of the centerwavelength of reflected light in the EUV wavelength region, i.e. itsrange (the difference between the maximum value and the minimum value ofthe center wavelength) being within 0.06 nm. Here, the in-planedistribution of the center wavelength of reflected light in the EUVwavelength region being within 0.04 nm, corresponds to the thicknessdistribution of the bilayer composed of two layers of a Mo layer and aSi layer, as the basic structure of the Mo/Si multilayer film, being0.04/13.53≈0.3%.

On the other hand, “Before correction” (dashed line) in FIG. 5 is agraph showing the relation between the location in a radial directionfrom the center of the substrate and the in-plane distribution of thepeak reflectivity of EUV light, when EUV light was applied at anincident angle of 6° to the Mo/Si multilayer reflective film formed bythe above procedure.

As shown by “Before correction” (dashed line) in FIG. 5, an in-planedistribution is observed such that the peak reflectivity of EUV lightlowers from the center of the substrate towards the peripheral portionof the substrate. The in-plane distribution of the peak reflectivity ofEUV light exceeds 0.6%, which does not satisfy the required valuerelating to the in-plane uniformity of the peak reflectivity of EUVlight, i.e. its range (the difference between the maximum value and theminimum value of the center wavelength) being within 0.5%.

Example 1

In this Example, a Mo/Si multilayer reflective film was formed as areflective layer 2 on a substrate 11 in the same manner as inComparative Example 1 except that a Si layer as the uppermost layer inthe Mo/Si multilayer reflective film was made to be a reflectivitydistribution correction layer having a thickness distribution providedin a radial direction, based on the in-plane distribution of the peakreflectivity of light in the EUV wavelength region obtained inComparative Example 1 (“Before correction” in FIG. 5) and the thicknessdependency of the peak reflectivity of EUV light shown in FIG. 3.Specifically the procedure was as follows.

The thickness of the reflection distribution correction layer (Si layer)at the peripheral portion of the substrate where the peak reflectivityof EUV light became lowest in Comparative Example 1, was set to be (4.5nm) in the vicinity of the thickness where the peak reflectivity of EUVlight becomes to have a local maximum value in FIG. 3. On the otherhand, at the center of the substrate where the peak reflectivity becamehighest in Comparative Example 1, the thickness was adjusted to thethickness (4.9 nm) corresponding to the decrease amount (about 0.6%) ofthe peak reflectivity of EUV light from the center towards theperipheral portion of the substrate.

With respect to the reflectivity distribution correction layer (Silayer) in the Mo/Si multilayer reflective film formed by the aboveprocedure, the thickness distribution in a radial direction from thecenter of the substrate was evaluated by means of XRR (X-rayreflectivity method). The thickness distribution in a radial directionfrom the center of the substrate was 0.4 nm, which substantially agreedto the difference between the thickness at the above substrateperipheral portion and the thickness at the center of the substrate.

As shown by “After correction” (solid line) in FIG. 5, as the Si layeras the uppermost layer in the Mo/Si multilayer reflective film was madeto be a reflectivity distribution correction layer having a thicknessdistribution provided, the in-plane distribution of the peakreflectivity such that the peak reflectivity of EUV light lowers in aradial direction from the center of the substrate towards the peripheralportion, was suppressed, and the in-plane distribution of the peakreflectivity became to be about 0.1%.

Comparative Example 2

In the same manner as in Comparative Example 1, a Mo/Si multilayerreflective film was formed on a substrate, and the relation between thelocation in a radial direction from the center of the substrate and thein-plane distribution of the peak reflectivity of EUV light, when EUVlight was applied at an incident angle of 6° to the Mo/Si multilayerreflective film, was evaluated. “Before correction” (dashed line) inFIG. 6 is a graph showing the relation between the location in a radialdirection from the center of the substrate and the in-plane distributionof the peak reflectivity of EUV light.

As shown by “Before correction” (dashed line) in FIG. 6, an in-planedistribution is observed such that the peak reflectivity of EUV lightlowers from the center of the substrate towards the peripheral portionof the substrate. The in-plane distribution of the peak reflectivity ofEUV light exceeds 0.6%, which does not satisfy the required valuerelating to the in-plane uniformity of the peak reflectivity of EUVlight, i.e. its range (the difference between the maximum value and theminimum value of the center wavelength) being within 0.5%.

Example 2

In this Example, the 3rd Si layer in the stacked number of repeatingunits of a low refractive index layer (a Mo layer) and a high refractiveindex layer (a Si layer) from the uppermost layer in the Mo/Simultilayer reflective film (i.e. the 3rd Si layer from the top) was madeto be a reflectivity distribution correction layer having a thicknessdistribution provided in a radial direction.

The thickness of the reflection distribution correction layer (Si layer)at the peripheral portion of the substrate where the peak reflectivityof EUV light became lowest in Comparative Example 2, was set to be (4.5nm) in the vicinity of the thickness where the peak reflectivity of EUVlight becomes to have a local maximum value. On the other hand, at thecenter of the substrate where the peak reflectivity became highest inComparative Example 2, the thickness was adjusted to the thickness (4.9nm) corresponding to the decrease amount (about 0.6%) of the peakreflectivity of EUV light from the center towards the peripheral portionof the substrate.

As shown by “After correction” (solid line) in FIG. 6, as the 3rd Silayer from the top in the Mo/Si multilayer reflective film was made tobe a reflectivity distribution correction layer having a thicknessdistribution provided in a radial direction, the in-plane distributionof the peak reflectivity such that the peak reflectivity of EUV lightlowers in a radial direction from the center of the substrate towardsthe peripheral portion, was suppressed, and the in-plane distribution ofthe peak reflectivity became to be about 0.1%.

Comparative Example 3

In the same manner as in Comparative Example 1, a Mo/Si multilayerreflective film was formed on a substrate, and the relation between thelocation in a radial direction from the center of the substrate and thein-plane distribution of the peak reflectivity of EUV light, when EUVlight was applied at an incident angle of 6° to the Mo/Si multilayerreflective film, was evaluated. “Before correction” (dashed line) inFIG. 7 is a graph showing the relation between the location in a radialdirection from the center of the substrate and the in-plane distributionof the peak reflectivity of EUV light.

As shown by “Before correction” (dashed line) in FIG. 7, an in-planedistribution is observed such that the peak reflectivity of EUV lightlowers from the center of the substrate towards the peripheral portionof the substrate. The in-plane distribution of the peak reflectivity ofEUV light was about 0.4%.

Example 3

In this Example, the 10th Si layer in the stacked number of repeatingunits of a low refractive index layer (a Mo layer) and a high refractiveindex layer (a Si layer) from the uppermost layer in the Mo/Simultilayer reflective film (i.e. the 10th Si layer from the top) wasmade to be a reflectivity distribution correction layer having athickness distribution provided in a radial direction.

The thickness of the reflection distribution correction layer (Si layer)at the peripheral portion of the substrate where the peak reflectivityof EUV light became lowest in Comparative Example 3, was set to be (4.5nm) in the vicinity of the thickness where the peak reflectivity oflight in the EUV wavelength region becomes to have a local maximumvalue. On the other hand, at the center of the substrate where the peakreflectivity became highest in Comparative Example 3, the thickness wasadjusted to the thickness (4.9 nm) corresponding to the decrease amount(about 0.4%) of the peak reflectivity of EUV light from the centertowards the peripheral portion of the substrate.

As shown by “After correction” (solid line) in FIG. 7, as the 10th Silayer from the top in the Mo/Si multilayer reflective film was made tobe a reflectivity distribution correction layer having a thicknessdistribution provided in a radial direction, the in-plane distributionof the peak reflectivity such that the peak reflectivity of EUV lightlowers in a radial direction from the center of the substrate towardsthe peripheral portion, was suppressed, and the in-plane distribution ofthe peak reflectivity became to be about 0.1%.

Comparative Example 4

In the same manner as in Comparative Example 1, a Mo/Si multilayerreflective film was formed on a substrate, and the relation between thelocation in a radial direction from the center of the substrate and thein-plane distribution of the peak reflectivity of EUV light, when EUVlight was applied at an incident angle of 6° to the Mo/Si multilayerreflective film, was evaluated. “Before correction” (dashed line) inFIG. 8 is a graph showing the relation between the location in a radialdirection from the center of the substrate and the in-plane distributionof the peak reflectivity of EUV light.

As shown by “Before correction” (dashed line) in FIG. 8, an in-planedistribution is observed such that the peak reflectivity of EUV lightlowers from the center of the substrate towards the peripheral portionof the substrate. The in-plane distribution of the peak reflectivity ofEUV light exceeds 1.6%, which does not satisfy the required valuerelating to the in-plane uniformity of the peak reflectivity of EUVlight, i.e. its range (the difference between the maximum value and theminimum value of the center wavelength) being within 0.5%.

Example 4

In this Example, a Si layer as the uppermost layer in the Mo/Simultilayer reflective film and the 2nd Si layer in the stacked number ofrepeating units of a low refractive index layer (a Mo layer) and a highrefractive index layer (a Si layer) from the uppermost layer (i.e. the2nd Si layer from the top) were made to be reflectivity distributioncorrection layers each having a thickness distribution provided in aradial direction.

The thickness of each reflection distribution correction layer (Silayer) at the peripheral portion of the substrate where the peakreflectivity of EUV light became lowest in Comparative Example 1, wasset to be (4.5 nm) in the vicinity of the thickness where the peakreflectivity of light in the EUV wavelength region becomes to have alocal maximum value. On the other hand, at the center of the substratewhere the peak reflectivity became highest in Comparative Example 1, thethickness was adjusted to the thickness (4.9 nm) corresponding to thedecrease amount (about 1.6%) of the peak reflectivity of light in theEUV wavelength region from the center towards the peripheral portion ofthe substrate.

As shown by “After correction” (solid line) in FIG. 8, as the uppermostlayer and the 2nd Si layer from the top in the Mo/Si multilayerreflective film were made to be reflectivity distribution correctionlayers each having a thickness distribution provided in a radialdirection, the in-plane distribution of the peak reflectivity such thatthe peak reflectivity of light in the EUV wavelength region lowers in aradial direction from the center of the substrate towards the peripheralportion, was suppressed, and the in-plane distribution of the peakreflectivity became to be about 0.3%.

REFERENCE SYMBOLS

-   -   1, 1′: EUV mask blank    -   11: Substrate    -   12: Reflective layer (Mo/Si multilayer reflective film)    -   13: Protective layer    -   14: Absorber layer    -   15: Low reflective layer    -   20: Sputtered particles    -   30: Center axis

The entire disclosure of Japanese Patent Application No. 2012-155453filed on Jul. 11, 2012 including specification, claims, drawings andsummary is incorporated herein by reference in its entirety.

What is claimed is:
 1. A process for producing a substrate withreflective layer for EUV lithography (EUVL), which comprises forming areflective layer for reflecting EUV light on a substrate, wherein thereflective layer is a multilayer reflective film having a low refractiveindex layer and a high refractive index layer alternately stacked pluraltimes by a sputtering method, and depending upon the in-planedistribution of the peak reflectivity of light in the EUV wavelengthregion in a radial direction from the center of the substrate at thesurface of the multilayer reflective film, at least one layer among therespective layers constituting the multilayer reflective film is made tobe a reflectivity distribution correction layer having a thicknessdistribution provided in a radial direction from the center of thesubstrate, to suppress and reduce the in-plane distribution of the peakreflectivity of light in the EUV wavelength region in a radial directionfrom the center of the substrate.
 2. A process for producing a substratewith reflective layer for EUV lithography (EUVL), which comprisesforming a reflective layer for reflecting EUV light on a substrate, andforming a protective layer for the reflective layer on the reflectivelayer, wherein the reflective layer is a multilayer reflective filmhaving a low refractive index layer and a high refractive index layeralternately stacked plural times by a sputtering method, the protectivelayer is a Ru layer or a Ru compound layer formed by a sputteringmethod, and depending upon the in-plane distribution of the peakreflectivity of light in the EUV wavelength region in a radial directionfrom the center of the substrate at the surface of the protective layer,at least one layer among the respective layers constituting themultilayer reflective film and the protective layer, is made to be areflectivity distribution correction layer having a thicknessdistribution provided in a radial direction from the center of thesubstrate, to suppress and reduce the in-plane distribution of the peakreflectivity of light in the EUV wavelength region in a radial directionfrom the center of the substrate.
 3. The process for producing asubstrate with reflective layer for EUVL according to claim 1, whereinthe in-plane distribution of the peak reflectivity of light in the EUVwavelength region in a radial direction from the center of the substratein a case where the thickness distribution corresponding to thereflectivity distribution correction layer is not provided, is anin-plane distribution such that the peak reflectivity becomes low in aradial direction from the center of the substrate, and as the thicknessdistribution in a radial direction from the center of the substrate inthe reflectivity distribution correction layer, a thickness distributionsuch that the peak reflectivity of light in the EUV wavelength regionbecomes high in a radial direction from the center of the substrate, isprovided, to suppress and reduce the in-plane distribution of the peakreflectivity of light in the EUV wavelength region in a radial directionfrom the center of the substrate.
 4. The process for producing asubstrate with reflective layer for EUVL according to claim 2, whereinthe in-plane distribution of the peak reflectivity of light in the EUVwavelength region in a radial direction from the center of the substratein a case where the thickness distribution corresponding to thereflectivity distribution correction layer is not provided, is anin-plane distribution such that the peak reflectivity becomes low in aradial direction from the center of the substrate, and as the thicknessdistribution in a radial direction from the center of the substrate inthe reflectivity distribution correction layer, a thickness distributionsuch that the peak reflectivity of light in the EUV wavelength regionbecomes high in a radial direction from the center of the substrate, isprovided, to suppress and reduce the in-plane distribution of the peakreflectivity of light in the EUV wavelength region in a radial directionfrom the center of the substrate.
 5. The process for producing asubstrate with reflective layer for EUVL according to claim 3, whereinthe thickness of the reflectivity distribution correction layer isadjusted to be such a thickness that at the peripheral portion of thesubstrate, the peak reflectivity of light in the EUV wavelength regionbecomes to have a local maximum value, and the difference between thethickness of the reflectivity distribution correction layer at theperipheral portion of the substrate and the thickness of thereflectivity distribution correction layer at the center of thesubstrate, is set so that the difference between the maximum value andthe minimum value of the peak reflectivity in the in-plane distributionof the peak reflectivity of light in the EUV wavelength region in aradial direction from the center of the substrate in a case where thereflectivity distribution correction layer is provided, becomes to be atmost 0.3%.
 6. The process for producing a substrate with reflectivelayer for EUVL according to claim 4, wherein the thickness of thereflectivity distribution correction layer is adjusted to be such athickness that at the peripheral portion of the substrate, the peakreflectivity of light in the EUV wavelength region becomes to have alocal maximum value, and the difference between the thickness of thereflectivity distribution correction layer at the peripheral portion ofthe substrate and the thickness of the reflectivity distributioncorrection layer at the center of the substrate, is set so that thedifference between the maximum value and the minimum value of the peakreflectivity in the in-plane distribution of the peak reflectivity oflight in the EUV wavelength region in a radial direction from the centerof the substrate in a case where the reflectivity distributioncorrection layer is provided, becomes to be at most 0.3%.
 7. The processfor producing a substrate with reflective layer for EUVL according toclaim 5, wherein the change in the peak reflectivity of light in the EUVwavelength region in a radial direction from the center of thesubstrate, formed by the thickness distribution in a radial directionfrom the center of the substrate, in the reflectivity distributioncorrection layer, is within 2%.
 8. The process for producing a substratewith reflective layer for EUVL according to claim 6, wherein the changein the peak reflectivity of light in the EUV wavelength region in aradial direction from the center of the substrate, formed by thethickness distribution in a radial direction from the center of thesubstrate, in the reflectivity distribution correction layer, is within2%.
 9. The process for producing a substrate with reflective layer forEUVL according to claim 1, wherein in the multilayer reflective film,the stacked number of repeating units of the low refractive index layerand the high refractive index layer is from 30 to 60, and at least onelayer among layers formed by the stacked number of repeating units beingat most 20 from the uppermost layer of the multilayer reflective film,is made to be the reflectivity distribution correction layer.
 10. Theprocess for producing a substrate with reflective layer for EUVLaccording to claim 2, wherein in the multilayer reflective film, thestacked number of repeating units of the low refractive index layer andthe high refractive index layer is from 30 to 60, and at least one layeramong the protective layer and layers formed by the stacked number ofrepeating units being at most 20 from the uppermost layer of themultilayer reflective film, is made to be the reflectivity distributioncorrection layer.
 11. The process for producing a substrate withreflective layer for EUVL according to claim 1, wherein the multilayerreflective film is a Mo/Si multilayer reflective film having amolybdenum (Mo) layer and a silicon (Si) layer alternately stackedplural times, and at least one layer among Si layers in the Mo/Simultilayer reflective film is made to be the reflectivity distributioncorrection layer.
 12. The process for producing a substrate withreflective layer for EUVL according to claim 2, wherein the multilayerreflective film is a Mo/Si multilayer reflective film having amolybdenum (Mo) layer and a silicon (Si) layer alternately stackedplural times, and at least one layer among Si layers in the Mo/Simultilayer reflective film is made to be the reflectivity distributioncorrection layer.
 13. The process for producing a substrate withreflective layer for EUVL according to claim 11, wherein a Si layer asthe uppermost layer among Si layers in the Mo/Si multilayer reflectivefilm is made to be the reflectivity distribution correction layer. 14.The process for producing a substrate with reflective layer for EUVLaccording to claim 12, wherein a Si layer as the uppermost layer amongSi layers in the Mo/Si multilayer reflective film is made to be thereflectivity distribution correction layer.
 15. A substrate withreflective layer for EUVL, produced by the process for producing asubstrate with reflective layer for EUVL as defined in claim
 1. 16. Asubstrate with reflective layer for EUVL, produced by the process forproducing a substrate with reflective layer for EUVL as defined in claim2.
 17. A substrate with reflective layer for EUV lithography (EUVL),which comprises a substrate and a reflective layer for reflecting EUVlight formed on the substrate, wherein the reflective layer is amultilayer reflective film having a low refractive index layer and ahigh refractive index layer alternately stacked plural times, and atleast one layer among the respective layers constituting the multilayerreflective film is a reflectivity distribution correction layer having athickness distribution such that the thickness increases or decreaseswithin a range of from 0.1 to 1 nm in a radial direction from the centerof the substrate.
 18. A substrate with reflective layer for EUVlithography (EUVL), which comprises a substrate, a reflective layer forreflecting EUV light formed on the substrate, and a protective layer forthe reflective layer formed on the reflective layer, wherein thereflective layer is a multilayer reflective film having a low refractiveindex layer and a high refractive index layer alternately stacked pluraltimes, and at least one layer among the respective layers constitutingthe multilayer reflective film and the protective layer is areflectivity distribution correction layer having a thicknessdistribution such that the thickness increases or decreases within arange of from 0.1 to 1 nm in a radial direction from the center of thesubstrate.
 19. The substrate with reflective layer for EUVL according toclaim 17, wherein the multilayer reflective film is a Mo/Si multilayerreflective film having a molybdenum (Mo) layer and a silicon (Si) layeralternately stacked plural times, and at least one layer among Si layersin the Mo/Si multilayer reflective film is the reflectivity distributioncorrection layer.
 20. The substrate with reflective layer for EUVLaccording to claim 18, wherein the multilayer reflective film is a Mo/Simultilayer reflective film having a molybdenum (Mo) layer and a silicon(Si) layer alternately stacked plural times, and at least one layeramong Si layers in the Mo/Si multilayer reflective film is thereflectivity distribution correction layer.
 21. The substrate withreflective layer for EUVL according to claim 19, wherein a Si layer asthe uppermost layer among Si layers in the Mo/Si multilayer reflectivefilm is the reflectivity distribution correction layer.
 22. Thesubstrate with reflective layer for EUVL according to claim 20, whereina Si layer as the uppermost layer among Si layers in the Mo/Simultilayer reflective film is the reflectivity distribution correctionlayer.
 23. A reflective mask blank for EUV lithography (EUVL), whichcomprises a substrate, a reflective layer for reflecting EUV lightformed on the substrate, and an absorber layer for absorbing EUV lightformed on the reflective layer, wherein the reflective layer is amultilayer reflective film having a low refractive index layer and ahigh refractive index layer alternately stacked plural times, and atleast one layer among the respective layers constituting the multilayerreflective film is a reflectivity distribution correction layer having athickness distribution such that the thickness increases or decreaseswithin a range of from 0.1 to 1 nm in a radial direction from the centerof the substrate.
 24. A reflective mask blank for EUV lithography(EUVL), which comprises a substrate, a reflective layer for reflectingEUV light formed on the substrate, a protective layer for the reflectivelayer formed on the reflective layer, and an absorber layer forabsorbing EUV light formed on the protective layer, wherein thereflective layer is a multilayer reflective film having a low refractiveindex layer and a high refractive index layer alternately stacked pluraltimes, the protective layer is a Ru layer or a Ru compound layer, and atleast one layer among the respective layers constituting the multilayerreflective film and the protective layer is a reflectivity distributioncorrection layer having a thickness distribution such that the thicknessincreases or decreases within a range of from 0.1 to 1 nm in a radialdirection from the center of the substrate.
 25. The reflective maskblank for EUVL according to claim 23, wherein the multilayer reflectivefilm is a Mo/Si multilayer reflective film having a molybdenum (Mo)layer and a silicon (Si) layer alternately stacked plural times, and atleast one layer among Si layers in the Mo/Si multilayer reflective filmis the reflectivity distribution correction layer.
 26. The reflectivemask blank for EUVL according to claim 24, wherein the multilayerreflective film is a Mo/Si multilayer reflective film having amolybdenum (Mo) layer and a silicon (Si) layer alternately stackedplural times, and at least one layer among Si layers in the Mo/Simultilayer reflective film is the reflectivity distribution correctionlayer.
 27. The reflective mask blank for EUVL according to claim 25,wherein a Si layer as the uppermost layer among Si layers in the Mo/Simultilayer reflective film is the reflectivity distribution correctionlayer.
 28. The reflective mask blank for EUVL according to claim 26,wherein a Si layer as the uppermost layer among Si layers in the Mo/Simultilayer reflective film is the reflectivity distribution correctionlayer.